A/N: My take on the Rose/Tentoo story we only got to see begin.

For those who like to keep track, this is season 4, post-"Journey's End" in the parallel universe and post-"The Waters of Mars" in the main universe. To the best of my knowledge, it's canon-compliant, including the Journey's End deleted scene where the Doctor leaves Rose and the Metacrisis with a TARDIS coral.

For those who don't, it should stand alone if you don't mind a bit of mystery. Comments, particularly on the flow, are always much appreciated.

As usual, when the Metacrisis Doctor woke in the dark, Rose was asleep.

She was still asleep when he dressed silently, navigating the room by the yellow light of the streetlamp through their window. Then, as usual, just as he reached the door and was sure he'd mastered the quiet slipaway, she rolled over and opened her eyes.

"Bananas in the break room fridge."

He grinned. One day he'd make a clean exit, but not today. "A fellow trying to sneak out could get a complex. Sorry."

"Mmf." She raised her head from the sleepy golden muddle of her hair to meet his eyes over the pillow, and smiled. "You all right, though?"

He came back and leaned over the bed to kiss her, at a rotational angle of 84 degrees. She was awake enough to cup his neck and pull him in, her other hand patting his shirt pocket to check that he'd gotten his specs. "All right. Just up. Look me up when you're in? If all goes well I may still be around."

She murmured something that might have been agreement, and was back asleep a moment later. A soldier's talent, that, coming instantly awake and then back down again. He had memories of mastering it long ago himself, but this body had had to learn it from scratch over the three years of its existence. Rose had honed it to mastery at Torchwood.

His 3 A.M. trips to the institute were the compromise they'd found between their human and his Gallifreyan physiology – their non-negotiable need for nightly sleep, and his peak capacity around five hours. The feel of the campus buildings at that hour was at once otherwordly and homelike - silent, dim, and weighty with the ceaseless feed of data from the sensor grid, always seeming just about to speak. With just the hurtling earth under his feet, the silent stars spinning in their ranks, and all the electronic ears of Torchwood like a kludged-together ham radio to the universe, those hours were the next best thing to helming a TARDIS.

With any luck, Rose would come in about daybreak, to ensure he and the building were both standing – "or lend a hand concealing the evidence" - and they'd have something worthwhile to talk through over tea. With any luck, this particular morning, it would be a breakthrough in graviton perturbation cartography of the neighboring dimensions, and he'd have a lovely comparative map of where the same neighboring stars lay in each of them.

Crossing pools of lamplight past the curtained terrace houses lining the two blocks to Torchwood, with stars overhead and bananas in the break room, he was filled as he often was those mornings with a kind of quiet triumph. They had started with mismatched ingredients and the vaguest of blueprints, he and she and this second-choice world. But with that weedy human resilience his other self admired, life had poked its tendrils up through the mess and started climbing. And, weedlike, it was nothing like he'd planned.

x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x

His first night under these stars, three years before, it had reared its head in his room upstairs from hers, at a beachside bed-and-breakfast whose reluctant manager had broken under Jackie's stare and found three vacancies after all. He'd been lying on his back in the dark, taking stock.

He had twelve hours alive and nine hundred years of memories. Some were glorious, some hilarious, and a few flared up on probing with a dazzle of pain that filled him with pity for his other self. Rose laughing at him; Rose shining with the light of spacetime, destroying and giving life; Rose clinging to the lever at Canary Wharf, fingers slipping into the Void; a blank wall with nothing on the other side.

He had a body count in the millions, a life sentence, and a ridiculous, impossible gift. He had been downstairs three times that night to check that she still existed.

That afternoon on the beach as they stared at each other, the TARDIS gone and the surf beating somehow unperturbed on the sand, she'd broken it first. "So, I'm sorry," she said wryly, "for denying you your identity, just now, in front of everyone you know in this world." She gestured down the surf toward Jackie with her free hand.

"Not at all; these things happen," he'd replied cheerfully, eyes on her, his heart still unclenching. Five minutes before, he'd stepped off the TARDIS expecting, since the moment he'd offed the Daleks, to spend his life alone in exile in this universe, with only Jackie to ring up to reminisce about the glory hours once in a while. Even that was pure kindness, his other self's sentimentality – another Gallifreyan would have destroyed him as soon as he was no longer needed, regardless of anything he'd done. Partly for being a mixed-species abomination, but mostly for the danger he posed to spacetime by knowing the true name of a Time Lord.

Yet here he was, and Rose was staying. One 'but he's not you' was a small price to pay. The thready spurt of joy he felt wasn't fair, but he couldn't quench it.

"And sorry," she'd added, not dropping his hand, "for the snogging ambush just after. You can press charges in this world too, if you like."

They'd both laughed there on the beach, hands clasped, in some dizzy mix of exhaustion, grief and hope. But she looked raw and wrung-out, and he'd wondered if his other self had just done something to her, with the best of intentions, that neither of their selves understood.

He would have asked her about it there, if not for the faint sense that some modicum of privacy should enter their relationship. That, and a nagging conviction that he needed to convince Jackie immediately that the TARDIS coral didn't stand a chance in this world, before she mentioned it to the Torchwood director she was married to.

Lying on the beaten-down mattress of the usually-unrentable attic room later that first night, he'd been under no illusions that anything was settled. Or, for that matter, that any of his memories of Rose had happened to this body. But at that time, he still thought like a Gallifreyan, reasoned like a Gallifreyan. The memories were real and they were his; ergo, really his. The proper ingredients were present: she and the TARDIS coral were here, and he had memory to be his scripture and signposts for a while. The rest could be sorted with time.

The attic hatch cracked open. Rose in a too-big borrowed t-shirt and sweatpants peered up, and the wash of warmth that lifted in him on seeing her felt entirely his own.

She lifted the hatch till the shaft of light fell across his face and she saw his eyes were open. She gave him a half-wry, half-embarrassed smile, brown eyes crinkling sweetly, as if to say, caught me. "Sorry." She started to back down.

He flipped on the bedside lamp, lighting the peaked pine rafters and the floor beams. "You, too? I've been down peering in your doorway every couple of hours." For weeks after Canary Wharf, I, he, would wake on the TARDIS, and whole seconds would pass before I remembered you were gone. Every time, for me, it all happened again.

She came up a few steps and flashed another smile; she was generous with them, he remembered. "We must be just missing each other."

He budged up to a sitting position, making the mattress creak ominously, and got a better look at her. There had always been something lush and generous about her face that made people see what they wanted to; usually, someone harmless, good for asking the simple questions that kept things clear in the midst of otherworldly chaos. That had bothered her sometimes, he knew; he wondered what she thought of her newer, angular look. It was more likely now that people would see a soldier.

Regardless, from the new steadiness about her, he had a dim sense that she had said "the Doctor will save us" for the last time long ago.

"Well, then," he said cheerfully, "want to consolidate? Save us both some walking." It was strange, saying that; even innocently as he meant it, as his other self he could never have made that offer to a mayfly living on his ship under his protection. He tossed the covers back and padded over to drag the little wicker couch closer. "Take the bed, if you like? I'm still not entirely sure if I need it."

In retrospect, he wasn't sure how many parts each of hope, loneliness, and kindness it was that she had stayed; he'd have to ask her. "All right, then." She slipped past him and under the quilt, searching his eyes in the lamplight. She looked just then like she had after his – well, essentially his - past regeneration, looking for something familiar in a new face.

It was his turn to break the silence. And it was always his turn to be cheerful in strange times. And he was desperately curious about the years they had missed. So he had asked her to tell him everything.

She told him about the long process of scoping out the character of this world's Torchwood, the secondhand joy of coming to know her not-father father, and how in the years since Canary Wharf she'd seen how the heart healed with time on its own accord, even against her will. She told him about their first giddy excitement over dimension cannon theory, and then the increasingly desperate work to make it reality as the stars began to wink out.

Then she decided it was his turn to tell all, and he prattled happily about the living sun and the Master and reuniting with the Ood, while she listened with the same old mix of one part fascination and one part limitless patience. And then they went further back, to the years where their memories were shared – the Sycorax, Cassandra, Krok Tor. It was bittersweet and marvelous; they laughed as if none of the darker things that had followed were even possible. He was auditioning for the role of himself. He didn't care.

A few of the stories did feel different even then somehow, as they talked through them; minor transient details that felt now like great gaping plot holes. He chalked it up to the bits of him that were Donna, finding their place in his mind. It didn't seem worth mentioning. They fell asleep with the light on.

He woke an hour later with his brain on fire.

The memories were going wrong. No, the memories were right, but his mind was wrong for them. It was in fact the Donna bits, but they were not going to settle quietly into a Gallifreyan mental order. They were going to burn the house down. They tossed up one memory after another at him, splayed it out, and then rotated it to a mad angle, like a kaleidoscope, the pieces all the same but the themes completely changed.

In the physical world, he sat bolt upright and gasped. Rose woke swiftly, blinked at him, and scrambled up to sitting, kicking the covers off. "Doctor? You all right?"

He turned to look at her, head pounding, and tried to say something reassuring. What came out instead was: "Jackie Tyler, alone in her council flat, watching the wall clock. The only person she loves in her world is out seeking adventure with a strange man who craves distraction more than life. She knows the world and how that story ends, despite everyone's best intentions, and there is nothing she can do. Because Rose sees her mother through his eyes now. And he finds her ridiculous."

Rose was accustomed to non sequiturs from him. She looked at him with mingled worry and regret, and seemed to consider her words. Finally she went with, "Yes. I know. But that was my fault as much as yours. His. Yours." She took a breath and tried again. "More my fault." She leaned over to study him. "You've got that Destroyer-of-Worlds look on. Are you all right?"

He took a deep breath and tried again. His single heart was beating wildly, off to one side; it was throwing off his balance. He forced himself to pull it together. "Me? I'm fine. Just a bit of mneumoneural reconciliation. The Donna bits are synapsing with memories of things they know they wouldn't have done. Perfectly natural. Right as rain in a few hours." He tried to smile reassuringly, wasn't sure he'd succeeded from the look on her face, and then lost it again when another one reared up.

"Sarah Jane Smith, alone on a world she's no longer fit for. Not sure why the center of her world never returned for her; just like a human, wondering what happened, she can't shake the fear that she fell short. The truth is somewhere in the mix in her head – he can't let anyone who knew him as a whole man see the wreck the Time War made of him – but she'll never know for sure, because it doesn't occur to him she's stuck like this, doesn't occur to send word. Move on. Move on."

Rose slipped over to the couch and sat beside him. "Can you put a stop to this? It's hardly fair; you didn't…" She trailed off, for which he was profoundly grateful, not saying, you didn't do any of it; you didn't exist. Losing claim to those memories was too high a price to pay for absolution from them. "You meant it for the best."

"Always do," he said as cheerfully as he could manage from under the rising tide of self-horror, and patted her hand. Another memory gripped him; he raised his eyes and met hers.

"Mickey Smith," he said. Her face fell; she dropped her eyes and he tried desperately to shut up, change the subject, but his executive function was a helpless bystander, waving from the windows as the tidal wave swept by.

"Focusing on carburetors and alternators to keep his eyes off the sky. His lover's off with another bloke, and it's not even quite that sort of love; apparently he's such a waste of a person that he lost her to an idea. But that's life; he could move on, but the bastard's filled her head so full of noble sanctimony, she doesn't even realize she's dumped him for it, so he can't be sure." He fought his way back to the helm for a moment. "Rose, I'm sorry. I'm so sorry. Don't listen; maybe it's best you leave. Come back in an hour. I'll be myself again."

"I don't think you will," she said slowly, and he knew she was right. She stroked his head like he was a small child; he closed his eyes and tumbled in the storm.

They came, one after another, flashes of the uncounted strangers and acquaintances tossed in his wake. In none of them was his other self deliberately hurtful; he simply, unforgivably, hadn't noticed. He was dimly thankful as he babbled that most of the others were only names to her.

Then it peaked, with the moments of that earlier afternoon, which flew apart and reassembled into a nightmare. His head jerked up; it hurt, worse than regeneration. He scrambled back from her, landed against the arm of the couch and stared at her, panting.

"Rose Tyler. Dropped on an alien shore with a dangerous stranger, and directed to transfer her love over to him like so much store credit. He may not be the man she moved time and space for, but that's all right, they both assure her. She should be glad for such a deal. Because he's really very like."

In the silence that followed, in the sudden bright well of tears in her eyes and her embarrassed effort to blink them back before he noticed, he knew it had hit home. He hated himself and his other self equally. With the glazes of memory and Time Lord self-assurance stripped away, he realized he was really seeing her for the first time, as she got her eyes clear and soldiered on. "Rose. I'm sorry. I'm so sorry. I should have said something. I didn't understand."

His disconnected executive functions were trying to make plans. He would leave. No. That was, apparently, what he always did. The only thing still clear was that he hadn't a clue what was good for anyone.

He was dimly, profoundly grateful his other self couldn't see this moment. It would have broken his hearts.

"No," she said gently, her voice closer. "He didn't either. I know that now." He could hear a strange relief in her tone; it meant something, having the way that moment had felt to her spoken aloud. She put one hand on the wicker back of the couch, a few inches from his. "But I would have fought him harder if I'd thought he was really wrong."

He looked back up at her in surprise. The understanding he'd resolved never to push on her was already there, likely grown over long years in this second world. For a dragon to love a mayfly cost the dragon almost nothing. But it would be, over time, desperately unfair to the mayfly. As a mayfly himself, or perhaps a square off the cube of a Gallifreyan consciousness, he knew his other self had done right to withdraw now, and would have been right even if he himself had never existed.

"Not a stranger, though," she said after a moment. "A new member of the family. With the family features."

He looked up at her. That was something. "You have to know…"

She raised her eyebrows, and there was a heartening cheekiness in her eyes. "…that he meant it for the best?"

"We always…he always does." The mneumal firing was slowing now, potentials equalizing across the new synapses. He pulled himself together, panting. "He couldn't have known what it was like for you. The Gallifreyan sense of the individual is a bit different. Regeneration, after all, you see."

"I do a bit, yeah." Her smile had changed in their years apart; there were more layers to it now, but he thought there was something genuine there. "This is already twice the personal talk you can usually bear at a time. Unless that's changed in the past hour, too?"

He laughed once, helplessly - "Ask me again in a few days?" – And she joined in. He took a breath; he had no idea how to live with the self he had inherited. Slowly he said, "I suppose it takes different virtues to live a life in place."

Rose gave him that reflective look again; there were any number of true things she could have said, and he waited for her verdict. Finally she said, "Courage still turns out to be a big one." And then she gave him a real smile. "So you're going to be brilliant."

He ducked his head, strangely embarrassed. "Well. I'll speak to Jackie in the morning." So many others I can never speak to, and him in their universe never knowing he should.

"She'll like that."

They were silent for a moment. Of all things, there was apparently a clock in the room, just now making itself heard, measuring out the moments of this single timeline.

Rose was searching his face again. "The part about you being dangerous. Blood and anger and revenge. Needing fixing." There was something competent and gentle in her eyes. "Was it a bit…cutting?"

He blinked away the fading memories and tried to focus on the concrete question, something solid to hold onto in the shifting sand of what sort of person he was. "Meant to be, I think. A heavy responsibility for you and a good dose of self-doubt for me. Tie us both down for a bit, keep either one of us from spinning off 'in the widening gyre', as it were, till our thoughts settle out. Gallifreyans, we're, they're, not rubbish at all aspects of human psychology.

"On the other hand. I committed genocide. I don't regret it. And that is frightening." He shook himself. He's too dangerous to be left on his own. He was not quite ready to decide what his other self's parting words meant to him, or the way he had fled that world whole minutes before he had to, so clearly appalled by what he'd made. Like a full-thickness burn, it didn't yet hurt. "Still, better me in this world than no Doctor at all, hopefully."

"The thing is," she said ruefully after a moment, "I'd have done the same." He blinked. "I did do, of course. A few years back. It was easier for him to forgive me than-" she gestured to him – "himself."

The metacrisis Doctor laughed, a bit grimly. "A bloodthirsty pair, we are." He took a breath; his one heart was slowing, heavy and perilously free at the same time. Nothing for it but to say it. "But I'm fairly certain I'm not bad enough to need the Bad Wolf to contain me." He looked down. "You've been chained to a blue box, one way or another, for long enough. Take your time. Figure out what you want."

She smiled. There was one part each in it of the Bad Wolf and of wisdom. Through the little garret window, the eastern horizon had grown faintly visible, and she turned to watch it come into focus. "I want." She glanced back at him. "I want…"

He caught on after a moment, guffawed, and got to his feet, only slightly dizzy. "Come on." He'd held out his hand, as memory told him he'd once held out a rougher hand on Earth, in a sea of people, the first time he'd asked her what she wanted. "Something must be open. Let's go find you some chips."

x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x

In the present, where he waved to the Torchwood duty station guard as he rounded the corner down the half-lit industrial hall to Applied Astrophysics, the Donna and Doctor bits of him seemed mostly to have made peace. They were together in his head, if nowhere else, and that was something.

He let himself in to the lab he'd taken over bench by bench, filling it with sensors lifted to the menagerie of signals like bird calls in the forest of the cosmos. It was a bit of a forest itself by now, cables crossing overhead between towered receivers on benches. The defensive benefits were clear enough to keep Torchwood motivated to keep the lights on. But the side effects were more to his purpose: humanity building up experience with the different voices of its nearest neighbors, learning what to take seriously and whom to trust.

He moved into the center, to the queen of the room, the graviton probe. She was a chimera of three centuries of cartography tools, controls and display screens, laid out in a rough chaotic circle round the central processor where a man could move round and reach them all. She was thrumming along in a test pattern, just re-mapping the stars in her own dimension.

The real challenge was still finding a way to validate their locations in the neighboring dimensions, without another vantage point outside Earth to compare results from. Possibly by mounting the probe on a space-going unmanned vessel. If he could miniaturize and harden the whole apparatus, if Torchwood was feeling flush, and if everyone was prepared to wait a year or two for results.

There in the silent half-lit fluorescence, as usual, he closed out the test pattern, turned the sensors outward, and swept the graviton probe like a flashlight down the hall of the multiverse to peer into its other rooms. The familiar triple ping of the search pattern started, one for each of the three dimensions of location for an object within its universe. The planetary bodies of the neighboring dimensions' Sol system equivalents swam into focus onscreen, each with its infinite duplicates down the dimensions, like reflections in facing mirrors out into eternity.

Of course, if it was going to take much more than a year or two to validate star mapping, it might be possible to just take the probe out for its second vantage in the daughter-TARDIS. But there were some things no Torchwood in any universe should develop a taste for access to in this millennium, and that was most of them.

Waiting, he sat back and looked round at the physical evidence of the give-and-take of his compromise with Torchwood. No weapons permitted in Applied Astrophysics, but the doors, walls, floors and ceilings were sheathed with Dalekanium, with shutters of the same for the windows, entrance controlled from the guard station, and isolable ventilation and power. If the world began to end, this room could hold out almost anything long enough to make a plan.

Not a bad show. Despite a bit of rough going at the start.

x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x

At his first meeting with Pete, in his first weeks on this world – achieved by poking round Torchwood like he owned it, periodically scribbling on a bit of paper, till the poor fellow called him into his office to prevent his being mown down by some panicky guard's rifle – he'd still been sick from the mneumoneural reconciliation. And sicker from having realized belatedly what, if it had been this bad for him, must have happened to Donna.

He was in no mood for mutual congratulations over saving the multiverse. It was time to take a swing at being this world's Doctor.

"I want to offer you a deal," he'd said, as brightly as he could, forcibly reminding himself Pete Tyler was a good man and a potential not-quite-father-in-law. "You've got all the heavy metals you need on this planet. You can build some lovely defensive tech."

Pete, hands clasped over the chaos of paper on his desk, ready a moment before with some cheerful small talk, had gone still, all business.

"Fields within which no nuclear reaction can take place. Some really brilliantly long-range sensors. Alien biometric detectors. Those, I can also test for you. Bzzt!" He grinned, but mirthlessly, and judging from the look in his eyes as he leaned back in his desk chair, Pete realized it.

"But?"

The Doctor dropped himself into the chair across the desk and leaned forward. "You've also got some very nasty stuff here." He pulled the crumpled paper from his pocket and pushed it across the desk. "This list is all the things that need destroying, very carefully. Let me supervise that, and I'll walk your people through the alternate tech, nut by bolt."

Pete took the paper wordlessly and scanned it. His lips tightened and relaxed as he moved from line to line. After a long moment he looked back up at him.

"I'm not certain," he said slowly, "which of us has more leverage here. And I hate to be this sort of ass. But experience with the other you tells me you'll give us the defensive tech when we need it, regardless. Even if I pointed every weapon on this list at the sky and left it running."

"Well, yes," he'd admitted freely, hands up. "You've got me there. No fooling Pete Tyler. No leverage at all. But there's still something you're missing."

Pete raised his eyebrows. The Doctor sat back and folded his hands behind his head. "Keep going with those lines of research, and you'll have your own Canary Wharf soon. Then perhaps every two to three years after. As I've no travel plans at the moment, naturally I'll do everything I can to help. But here's what you're not considering."

He pulled out the sonic screwdriver he'd purloined shortly after offing the Daleks, in anticipation of his permanent stopover. His other self must certainly have noticed, but had courteously said nothing. No matter; cut off from the TARDIS, it had stopped doing anything but glowing a week later. "You know one Doctor and what he'll do if you accidentally tear the universe open. Appear out of nowhere with a mad plan, and save the world with the TARDIS and the wonderful things inside. But the Doctor in this world?" He pointed the screwdriver downwards between them. A little dancing blue dot appeared on the desk. "He has a penlight."

He popped the screwdriver back in his pocket, jumped up, shook Pete's hand vigorously and turned to go. "Think it over. I'll be around." He hesitated. "Possibly at the dinner table. I'll try not to make it awkward."

Pete sighed behind him. On that, they were in perfect accord.

At the doorway, something else occurred to him, and he turned back. "Also, I'd like a credit card. With money on."

Nonplussed, well on his own way to getting accustomed to him, Pete only said, "How much?"

He hadn't thought that far. "Oh, well, whatever's enough for bananas. And a pair of brainy specs. And some of those chips she likes."

His one heart was pounding when he closed the door behind him. But then, his other self had usually seemed cooler in planet-changing negotiations than he felt, too.

They'd shaken hands on it later that week; he'd begun his gradual takeover of the Applied Physics lab in the months that followed, and had the idea for the graviton probe a couple of years after. ("Pete, your own theorists have already stumbled into this. Go and ask them. Have you never wondered why gravity is so much weaker than the other fundamental forces? Gravitons go absolutely everywhere, diffusing their power over any number of dimensions. And we're going to watch them do it.")

x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x

The probe squawked.

Four months of searching out the neighboring planets and nearby stars in other dimensions, turning up readings consistent with everything from black holes to asteroid belts, and this was the first time linear motion detection had gone off.

A good thing, too, until now. A mass effect big enough to detect, making a linear transit, was unusual in a star system, where objects generally preferred to move in circles. Either a chunk of planet escaping orbit and most definitely large enough to be missed, or a fleet of ships going somewhere intentional, of a collective size that was only sensible for one purpose.

He switched over to the quadruple ping of linear tracking: the three for the object's location, and the fourth along its predicted path, to confirm it showed up as expected.

The object was moving past a planetary body – the Mars analogue, by mass. As the fuzzy monochrome light of the display focused in on it, the hairs on his neck prickled. Higher mass density in the core, lower toward the edges, but the gradient was too linear to be a natural body. It was a war formation - keep the big ships in the center. Death on engines, three to eight universes over based on the recoil time.

He felt like a man leaning over a bridge rail to look into a fish pond, and seeing a school of barracuda swim purposefully by below.

Then, slowly, the mass signature spread out and began to dissolve, from the edges inward. Over 8.2 seconds, by his approximate halfbreed time sense, it melted away into nothing.

Better no war fleet than one war fleet, he supposed, but the process was less than reassuring. Feeling vaguely paranoid and ridiculous, he jumped up from the probe and darted round the room, checking the motley assortment of more humble this-universe-only sensors to convince himself the fleet hadn't reappeared in his own world. No, only spread out from each other, and each individual ship was too small for the probe to detect.

That was why he almost missed it.

A lance of graviton perturbation on the probe display sliced out of nowhere, anchored itself in the Mars-analogue planet in a motion absurdly like a grappling hook, swung from the planetary contact point, and vanished. He felt a sudden, nameless unease.

Immediately the fleet coalesced again, tightening to a small dense knot, back in a linear beeline to the lance's point of origin. As he watched, it overshot, doubled back restlessly, and gradually dissolved again.

"Hello," he murmured to no one. "Trouble finding your target? Slippery little fellow."

Minutes passed. The fleet dissolved again – spreading out to search, he assumed. The graviton perturbation lanced out again from a different point; the fleet reconverged on it. At a guess, whatever was sourcing the lance was using the planet as an anchor to reposition itself to evade the searchers, like swinging from vines.

A drama, or romp, or exercise playing out in the Sol-analogue system, queasily close to that dimension's Earth-analogue but not focused on it. And none of it done with present-day human technology, unless something extraordinary was happening on that Earth.

Watching the flash of the lance and the answering fleet coalescence, repeating every few minutes as the quarry dodged about, he finally realized why he felt so uneasy.

Any number of species might pass through the effective range of the graviton probe, roughly the solar system's diameter. Only one was likely to hang about a nearby dimension's Earth, travel as a single ship, and use gravity as its rappelling harness as if its people had invented black holes.

One easy way to find out.

The metacrisis Doctor gave himself one breath, surprised and a bit ashamed of the ridiculous, roofless dread that had settled on his shoulders. Then, without changing the line of sight, he set to modulating the beam power. Only one species, too, would be able to receive and interpret a graviton beam bearing a nineteenth-century Earth Morse Code transliteration of modern Gallifreyan.

He delayed another 1.7 seconds, debating what to send.

Wrapping up world domination here; next stop, yours. Too bitter, and without the option of tone, rather cruel.

Do you require assistance? Dimensions apart, the jumpers defunct, no way to do more in that universe than rap on the glass, that would be even crueler.

And the one he actually sent, across the worlds to the not-himself other self who had fashioned him in his image like a footprint from a boot: Is that you?