Author's Note: Aaaaand, here it is, the challenge many of us set ourselves at some point: taking an existing episode and rewriting it to suit our purposes. My chosen target: End of Time (with a sideswipe at Waters of Mars for good measure). Let's see how I do. Reviews always welcome!

This is the third entry in my series John & Mike & Rose & Donna. As always, new readers are *strongly* urged to begin with the first story (you can find it through my profile). I'll be sprinkling reminders in for returning readers, but they're no substitute for the full backstory. (I'm trying not to waste as many words as I usually do on Fill-in.)

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Chemistry

Element noun 1. Chemistry: one of a class of substances that cannot be separated into simpler substances by chemical means. See also chart under periodic table.

^..^

"Scorch it!" The Doctor was quite thoroughly annoyed; the TARDIS rarely disappointed him like this. "I'm sorry, Rose, Davey. I could have sworn we had more space suits than this!" Waving a dismissive hand at the old orange suit from Krop Tor, he cast a last hopeless glance around the vast wardrobe before giving up. "Well, never mind, then. We'll just go somewhere else." He began stumping morosely towards the stairs; he'd really wanted this expedition.

The witnesses to his displeasure gave each other a conspiratorial glance, reassuring each other wordlessly of their like-mindedness: they weren't all that disappointed at this turn of events. "Hey, wait, Doctor! That's OK. We're fine. You go on ahead and explore the old station, we'll stay here and have a school day." Rose stopped her husband's petulant stomping, swinging him around and pulling his head down for a smooch.

"But... I wanted to show it to you, too! Don't you want to see it? The very first off-world colony?"

"Not without a space suit!" She grinned at him. "Go on, we're fine. Have fun!"

"Davey?"

"Yeah, go on, Dad."

"Wel-l-ll..." One last hesitation for show, and he capitulated, bounding over to the orange suit and pulling it on over his old pinstripe. "What is today, anyway, Assistant Professor? Maths? Literature?"

"Nope! Today is Search Day! But we need a new target, Professor."

"Oooooh, let's see, target for Mars, target for Mars..." He zipped up the suit and tilted his head back, contemplating, the tip of his tongue stuck behind his upper teeth in the way he knew drove Rose dizzy – glancing sideways at her under his lashes to make sure it was having its usual effect. "Ah! I have it. Elements!"

"Elements? As in, elementary, my dear Doctor?" Sure enough, her tongue tip was peeking out between her teeth, driving him dizzy in return.

"Na-ah! Too easy, no points, so sorry!"

She stuck her tongue out the rest of the way, impudent. Laughing, the Doctor picked up the helmet and ran down the steps back to the control room, stopping to throw a couple of switches on the console before striding to the door. "There! I've extended the force field out ten feet so you two can at least step out the door. Mind the limit, now!" Suddenly tender, he turned and scooped Rose up for a kiss. "I won't be long." He waved at Davey back at the console (his nine-year-old dignity too much for too many affectionate embraces from his parents), then Rose helped secure his helmet, and he was off, bouncing across the Martian landscape towards the rocky ridge on the horizon.

Davey walked down the ramp to watch him go, and after Dad turned on the ridge for a last wave before disappearing down the other side, he stepped out the door onto the red sand and knelt down, scooping up a handful of it. "I know number one already, Mum: chemistry. The periodic table we learned last year. Let's take this to the lab and analyze it."

She beamed at her son. "Good one! And while that's running, we'll hit the dictionary for some more."

Truthfully, since they had made it back from Pete's World five years ago and begun traveling again, she had been enjoying her son's highly unorthodox education immensely. She often thought she was learning as much as he was. In fact, she sometimes suspected the Doctor (he had, indeed, left "John Smith" behind in the other universe for the most part, returning to the name he'd been using for centuries) of deliberately engineering the curriculum to make up for the huge gaps in her own education – though she never asked him about it. She didn't really want to know.

They usually spent the entire day on a single subject rather than dividing their time and attention up. Search days were some of the most fun – the Doctor would give them a target word or concept, one with many varied meanings, and she and Davey would hunt through the TARDIS library, databanks and labs for all those meanings, coming up with as many examples, extensions, shadings, and consequences as they could. The more points they earned, the bigger the ice cream sundae or other treat with which they celebrated at the end of the day. It was an exiting way of tying together an impressive array of subjects, starting with linguistics, of course, but they never knew what avenues and side alleys the search might take them down.

They stepped back inside the TARDIS, Rose closing the door carefully behind them, and took the Martian soil to the lab for analysis. Then, "to the library!" became the battle cry, and the Search was on.

^..^

Several hours later, Rose left Davey in the library, immersed in comparing several volumes of various philosophies, and puttered her way towards the control room, doing Mum stuff: picking up discarded bits of clothing and tossing them in general bedroom directions, quickly rinsing the lunch dishes, etc. She was just pulling up the outside sensors on the main screen and picking her way through her meager Gallifreyan (politely refusing the TARDIS's offer of translation) to see if she could locate the Doctor, for practice, when the man himself burst through the door, ripped off his helmet and threw it hard against the wall. The crunch told her it was going to need repair before it would be usable again; just as the thought crossed her mind, it fell into place beside the look on his face as confirmation that her husband was seriously disturbed and upset.

"Where's Davey? Inside?" He barely glanced at her, sweeping up to the console and tearing into pre-flight. No sooner had her "yes" left her lips than he threw the lever and spun them into the Void. Then he completely shocked her by suddenly pounding both fists down on the edge of the console and letting out a strangled scream of frustration and fury. "You stupid, stupid machine! Why did you do that to me? Why did you take me there? Why?" Raising his head, he glared at the Time Rotor with such anguished reproach that Rose glanced to make sure the sledgehammer was out of his reach.

She softly stepped over to his side and tentatively touched his arm, and when he didn't flinch away, turned the touch into a gentle hold. "Doctor? … John? … What happened?" He shook his head, unable to articulate at the moment, but didn't shake her off, so she pulled him around, and then led him over to the huge, low curved couch they'd added against the wall behind the pilot's jump seat. He let her unzip the space suit and shimmied out of it, then collapsed on the cushions, and she crawled up and wiggled behind him, wrapping him up in her arms as he snuggled into his loving, human cushion.

Over the next few minutes, her warmth and love seeped into his slender frame, relaxing and soothing him. He twisted up and around to kiss her a thank you, then settled back again, finally able to take a deep breath and explain. "The TARDIS missed my target time. I was aiming for twenty sixty-nine, but it brought me to precisely November twenty-first, twenty fifty-nine instead. The very day the Bowie base was destroyed – the first human colony." Another deep sigh. "I met them, Rose. I met every one of them. They were all so wonderful, so brilliant, so alive. But I couldn't save them. I had to let them die. It's a fixed point in time, their deaths, with so many future events dependent on them – the entire future course of human space exploration. I couldn't... I wanted to, so much. God, it hurt so much to walk away. But I had to. I had to..." His voice trailed away into a shuddering sob, and two tiny tears dripped unmentioned.

Humming softly in sympathy, she stroked his hair and whispered, "I'm so sorry, love." She knew better than anyone how much he cared about everyone he met. After a couple more minutes of silent companionship, she had an idea. "Tell you what. Let's go home for a bit, back to the shop. I'd like to see Mike and Donna and the kids, and just be normal for a bit. We haven't visited in a while. Besides, your brilliant son needs new textbooks soon; he's almost done with the ones we have." She chuckled softly. "At this rate, he'll be graduating from an Earth college before he's twelve."

The Doctor grinned up at her, slyly. "Which would make him right on track for a Time Lord's son." He sighed, then nodded. "Sounds good. Remember Elizabeth it is." He wouldn't say so, but he absolutely loved the name his twin and sister-in-law had picked out for their used book shop back on Earth, in honor of Elizabeth Bennett of Pride and Prejudice. He turned his head, rubbing his cheek against her chest like a cat. "Do we have to go right this second, though, Mrs Smith?"

She purred. "Why, do you have something else in mind, Mr Smith?"

Grinning, he began to turn to make his suggestion, when out from the doorway stumbled Davey, red-eyed and sobbing. "Mum! Dad!"

Startled, they both reached out to him as he half-ran to the couch, pulling him into their cuddle. That he didn't resist spoke volumes about his distress. "Davey! What's wrong, sweetheart?"

"I... I had a nightmare."

His parents gave each other a puzzled look. "It's the middle of the day!" remarked his father.

"I was reading Chinese philosophy, and I guess I fell asleep."

The Doctor grinned. "Well, that stuff would put anybody to sleep." His look softened, and he put a hand on Davey's head. "What was your nightmare about?"

"I.. I don't really remember now, it's fading. But there were three men. Three different men, over and over, flashing through my head one after the other."

"What men? Do you know any of them?"

The boy thought for a minute, carefully, trying to bring the faces up clearly. "No... I don't." His face twisted. "I'm sorry, Dad, it's fading. I can't remember now." He sat up straight, pulling away slightly, and rubbed his face. "I'm sorry. Stupid, getting all upset over a silly dream. I'm not a kid any more."

The Doctor's hand had slipped off his head as he pulled away; he put it back on his son's shoulder and gazed at him seriously. "No, but you're part Time Lord, and sometimes dreams are full of real meaning, not just stray images. The more a dream affects you emotionally, the more significant it is. Could be some very important information slipping into your mind from any number of avenues. If you remember anything else about it, or recognize any of the men, let me know right away, all right?"

Davey gave a last sniff, and nodded, solemn. "OK. I will."

His dad grinned, and ruffled his hair. "Good. As a matter of fact, Mum and I were just deciding something. How does a trip home to the shop sound? Would you like to visit Uncle Mike and Aunt Donna?"

His immediate, happy grin was answer enough.