"You routed the doubters, and you scattered the gloomsters, and for the first time in living memory you caused tube-train passengers to break into spontaneous conversation."

Lucas smiled as Ros joined the small knot of officers watching the news channel re-broadcasting the mayor's speech at the Victoria Memorial. He handed her a mug of coffee.

"You have to admit it, he's got something. He had those crowds eating out of his hand."

"… such paroxysms of tears and joy on the sofas of Britain that you probably not only inspired a generation, but helped to create one."

As laughter rippled through the group, Ros caught sight of Harry, with his usual Ruth-shaped tail, emerging from his office and pointing towards the conference room. "All right, break it up," she said mildly. "It was funny the first ten times. Back to work." She gulped down the coffee. "Where's the latest report from CO-19 at the pub?"

"I'll find out." Lucas strode away to the tech suite as she crossed swiftly to the meeting room. Preliminary reports from bomb disposal indicated that no explosive device had been found, but after evacuating the building, they had cordoned off two blocks in both directions on Ros's orders in order to go through it with a fine toothcomb. Alex Pemberton's body had been removed discreetly to St Pancras' Mortuary, to where the pathologist on call to Thames House had been sent post-haste, and Chen Liu had accompanied two police officers to break the news of his son's death to Sir Roger. Everyone else had been ordered back to base once the parade reached the VIP area in the Mall and was handed into the care of a troika consisting of the Met, the Diplomatic Protection Group and the army. As the crowds began to disperse, the day's celebratory ambience, overlaid with an intense feeling of relief, had gradually begun to permeate Thames House too. Ros would have liked to share in it, but although the trees might be thinning, she knew they weren't out of the woods yet. Yes, the parade had been a huge, safe success, as the Mayor had promised. And they could certainly boast of a Triumph with the arrest of Asif Iqbal Mahmood. But the as yet unannounced death – murder – of Alex Pemberton was a huge blow. Harry was withholding the information until the athlete's father had been notified, but it would have to be released sooner rather than later, and she could just imagine the Home Secretary's reaction. And although she would have been the last person to rejoice at finding a bag of uranium glowing sweetly green under Samuel Pepys' favourite seat in Ye Olde Cock Tavern, the fact that they hadn't meant that it – and a potential Disaster - must still be out there somewhere. The threat wasn't yet contained … just deferred.

"Where's Khalida?" Harry asked, as Ros slid into her usual seat, and Lucas, Ruth and Callum settled in around the table.

"I sent her to Paddington Green," Ros answered. "Just to observe procedures for Mahmood and the rest of his merry men; check what other rotten fish we may have caught in the net."

He nodded. "Right, then first things first. That note on Pemberton's chest."

"It's a Biblical quote, Harry. Revelation, chapter eight." Ruth glanced down at the notepad in front of her. "A great star fell from heaven, blazing like a torch, and it fell on a third of the rivers and on the fountains of water. And - " she hesitated, and checked the paper again.

"And the star's name was Wormwood." It was Lucas who finished the quotation, and Ros suppressed an involuntary smile. The combination of a photographic memory and being the son of a Methodist minister occasionally gave Lucas a head start over the rest of them when it came to dealing with the world's religious fanatics. Then, belatedly, she noticed that he had turned sheet-white.

"Lucas, what is it?" Harry had noticed too.

The younger man swallowed hard. "Wormwood. I – er - I think it's a message, Harry. They're taunting us."

"Meaning?" Harry snapped.

"Chernobyl. The reactor explosion in '86. The word chernobyl – it's a type of plant; you find it in Russia and Ukraine. " He paused for a second. "And Belarus. Mugwort, I think, in English. Anyway, it's a type of wormwood. I remember Vyetochka telling me. The Russians are incredibly superstitious, read signs into everything, and a lot of people at the time linked up the Biblical reference and the accident's release of - "

"Uranium." The word came out through gritted teeth, and Ros tensed. She would have loved to think Lucas was just being whimsical, but the choice of that particular quote from the many apocalyptic descriptions available in Revelation couldn't possibly be a coincidence.

"What's the situation at the pub now?"

"It's clear, Harry." Callum flicked a finger expertly across his iPad. "They've turned it inside out and done a fingertip search of the immediate area. The Broken Arrow team's not found a trace of radiation anywhere."

There was a momentary silence. Then Ruth ventured: "Well, that - that's good … isn't it, Harry?"

Yes, Ros thought. And no. It only meant that they knew where Mahmood hadn't planted the bomb. Those lines were a taunt all right … and a threat. She looked at Harry, who didn't appear to have heard Ruth's question; he seemed lost in his own thoughts. There was a strained pause, in the course of which six anxious eyes turned towards Ros. She cleared her throat.

"Harry, do you - "

"Was anything suspect found on him?" He interrupted her by firing the question at Lucas, his face a picture of frustration. Lucas shook his head uneasily. "Then it's still out there. Somewhere. Ruth, get hold of the Commissioner and the chief ops officer for the Met. Now!" He rapped his knuckles on the squawk box in the centre of the table, and Ruth shot out of the room as if the Wormwood Star itself was chasing her. "I want that whole area searched from end to end."

"They did that, Harry. Before it was sealed off," Callum interjected.

The glare Harry shot him would have felled a less solid ego."Then I want it done again. To be in there, he must have got in through the access points either at the top of Fleet Street or at Aldwych. If he planted that bomb it's in there somewhere between the two. We have to find it."

If, Ros thought. She met Harry's eyes. Unspoken and certainly unwanted, the 'M-word' was creeping into her mind. She wondered if it was troubling him as well.

"Harry, he's still on his way back to the Yard. And the ops officer's not available." Ruth's information elicited a minor explosion of Anglo-Saxon that needed no translation, and she cringed. "They'll have him on the line as soon as he gets back."

"Well in the - " Harry stopped in exasperation as Ros's mobile rang. Ros made a moue of apology and then read the screen. Khalida calling. She put the phone on loudspeaker and replaced it on the table. "Go on, Khalida."

"Ros, I am still at Paddington Green." There was a cacophony of voices in the background to the call, making it difficult to catch her words. "Wait – just a moment." When her voice returned, it rang out more clearly. "Sorry, it is jolly hectic here."

"No worries. Are any of that group on the Watchlist?"

"Yes. Two, so far. But that is not the problem." They all heard her gulp. "It is Mahmood."

"What about him?" Ros asked, trying to keep her steadily rising tension out of her voice.

"Something is wrong, Ros - very wrong. It – you see, he is not Mahmood."

There was a second's stunned silence before a gasp of disbelief sped around the table. Harry leaned towards the phone. "Explain yourself!"

Khalida's voice sounded nervous at the barely-contained fury in his. "It was the identification procedure, Harry. Special Branch has Mahmood's fingerprints on file, and the prints of this man do not match them. They have taken a DNA swab, and it is being processed in the police lab now."

"Then they aren't sure?" It was Lucas who asked the question, but Ros knew it was more in hope than expectation.

"Almost, because there is more." Khalida, probably anticipating the reception they would get, was clearly reluctant to utter her next few words. "When they were asked to undress, this 'Mahmood' was found to be five feet ten. Asif Iqbal Mahmood is a little over six feet. He was wearing something in his shoes to give him the extra height, Harry."

That clinches it. There were ways of making a man look taller, but it was impossible to reduce anyone's height by three inches. Suddenly, Ros felt chilled through, and her nails dug into her palm.

"Have they any idea who he is?" Harry barked.

"No, sir. His prints are not on their files. He has given a name, but it is not one of which they have any record, and I very much doubt that it will be the real one."

Ros watched Harry's right hand slowly clenching into a fist. Without warning, it smashed down onto the table with such force that her phone was almost knocked to the floor. She grabbed it just in time.

"Right. Tell the SB I want him held for conspiracy under the Prevention of Terrorism Act. And the rest of them. As soon as the SB has the results of that swab back, I want them e-mailed straight over to us. You stay until the identification procedures are completed, and and then I want you back here. Understood?"

"Yes, Harry." There was a slight quiver in Khalida's voice that Ros interpreted as fear of falling victim to shoot the messenger syndrome. She flicked off the loudspeaker and picked up the phone.

"Well done, Khalida." She tried to add some reassurance to the crispness of her tone. "We need you on the Grid now, soon as you can, OK?"

"Yes." Khalida hesitated. "Ros, have we been taken to the fairground?"

It took Ros a moment, and when she worked out the question, she longed to be able to give a convincing denial. She literally had to force the words out.

"It's possible. Hurry back."

"But … how can that be?" Ruth asked, as the call ended.

"That bloody original footage from the closing ceremony." Callum almost spat the words out as he turned from her to Harry. "Remember how we couldn't get a proper match with the face recognition? I said then that it looked as if he'd altered his appearance somehow – probably with plastic surgery." His eyes narrowed into glittering slits. "Son of a bitch."

"Then – then this was deliberate?" Ruth looked from one to the other. "So Mahmood was … what – using this man as a substitute?"

"Or a decoy," Lucas said quietly. Ros looked sharply at him. She still wasn't sure what track Harry's mind was taking, but Lucas's was clearly following the same path as her own. "If he deliberately changed his appearance to be almost identical to this man then they've been planning this for a long, long time."

"They couldn't have been," Ruth objected. "The parade was only formally announced last week."

Lucas shrugged. "Yeah, but the idea's been in the air for ages. Maybe they tweaked the plan. Once the Games themselves were over security got a bit slacker, people started to relax … they probably thought it would be a softer target."

"The why of what they've already done isn't important now," Ros said firmly. She knew that talking was a way to cope with the shock Khalida's report had dealt to everyone, but they had to get back on track. "It's the how of what they might still be intending to do we need to focus on." She looked at Harry, who had contributed nothing but a profound, stone-faced silence since the end of the phone call. Formally, she had been stood down as Gold Commander when the field operation ended. "Harry?"

There were a few seconds of silence during which she wondered whether he was going to answer at all. Then he lifted his head.

"Ruth, I want a secure call to either the Commissioner or his ops chief within the next five minutes. No delay, no excuses, tell the Yard it's a red call. Callum, get hold of that PPS at the Home Office, what's his name - "

"Beckenbridge," Lucas supplied.

Harry jerked his head in acknowledgement. "Beckenbridge. Scramble it. When you've got him, tell him to hold." He got to his feet with a brusqueness that sent his swivel chair shooting backwards against the wall with a clang of protest. "Lucas, find out what the hell's taking Chen so damned long in Kensington; I don't want Pemberton giving people the willies in Whitehall. Ros, come with me."

Ruth and Callum scrambled up and followed him. Callum even dropped his iPad in his haste, which was a more vivid illustration to Ros of their shared and swelling sense of urgency than a dozen red calls would have been. The feeling of quiet Triumph that had been seeping onto the Grid was already crumbling under its weight. She turned for the door, and then felt Lucas's hand on her arm.

"Misdirection?" he murmured.

There it is. The M-word that had been lurking in the wings of Ros's mind for the last twenty minutes, suddenly centre-stage and in the limelight. She bit her lip. "Maybe."

"Shit," Lucas said with vehemence. "The bomb could be anywhere in that section."

Or nowhere. A shiver ran through her and knowing how observant Lucas was, she folded her arms to prevent another. Too late.

"You all right?" he asked sharply.

"Of course," Ros lied. "Air-conditioning." Lucas was as likely to swallow that as she was to believe that he'd developed a sudden passion for high diving, but she didn't want to explain the growing feeling of dread causing her to tremble. If Asif Iqbal Mahmood's doppelganger had been there to draw their eye to him, the pub and its immediate environs, which now seemed hideously likely, then just how far had the terrorists' trompe l'oeil gone? Could they safely circumscribe it just to the stretch of the City between Fleet Street and Aldwych? Pemberton's death did seem to follow the pattern of the terrorists 'mopping up' behind them. Assuming that he had been coerced into helping them plant the bomb, he would never be able to reveal its location to MI-5 now. But the parade – its target – was over. It doesn't make sense. Except in one way - one that brought the spectre of Disaster out of the shadows to loom large over the Section like a ghastly mushroom cloud.

"Rosalind!" At the irascible bellow, both hurried out, Lucas heading for his desk, and Ros hot on Harry's heels. When she followed him into the office, he growled: "Shut the door." He looked at his watch. "They've got two minutes."

Ros hesitated. She had always trusted Harry, even when they disagreed with each other, and she knew the feeling was mutual. He had never objected to her querying a decision, provided she could back up her query with facts. The problem here was that she didn't have any, just an intensifying, icy dread that they were about to turn in a wrong and potentially catastrophic direction. Harry wouldn't change his mind just because of the knots in her stomach or the shivers down her spine. She moistened her lips and took a deep breath.

"Are you sure we need another search, Harry?"

The look with which he impaled her was so hostile that Ros could almost smell the sulphur.

"Aren't you? What, are you suggesting that we just sit and wait until half of the City becomes a wasteland fit only for experiments with mutant forms of plant life?" His telephone rang. "Pearce. Yes, Ruth. Good, put him through."

"Harry, wait! Listen. Give me a minute; just let me explain. Put him on hold – please!" She swallowed. Appealing to someone's better nature – even Harry's – didn't come easily, but somehow she had to make him listen. She went for the jugular. "Trust me, Harry."

She watched concern blur the edges of the impatient anger on his face as the uncharacteristic pleading note in her voice reached him. He hesitated, then snapped into the phone: "Five more minutes, Ruth. Have them hold." He turned back to Ros, still holding the phone. "Out with it."

Ros plunged in. "Harry, the parade's over, the crowds are starting to leave the area. If the bomb was there somewhere and they were going to detonate, they'd have done so by now. They'd want a spectacular, you said so yourself. A double impersonating Mahmood, the break-up of a noisy demonstration calculated to look as if it was there to provide him with cover to direct our focus onto him - and that area. I don't think the bomb's there." Now the most delicate bit, the bit he really won't want to hear. "I don't believe the parade was the target. I think we've been misdirected, Harry."

For thirty seconds that felt endless she held his gaze, willing him to accept the possibility. Her words hung in the air, poisoning it, Ros thought irrelevantly, more effectively than any wormwood, celestial or otherwise, could poison water. When Harry raised the phone to his ear, still watching her, her vision blurred ominously and a sudden buzzing filled her ears. His words had a metallic echo to them.

"Ruth, cancel the call. Stand them down. False alarm, and convey my apologies." He hung up. "Sit down. I don't allow swooning in the office." He pointed at the chair in front of his desk.

Ros groped her way into it and lowered her head for a moment to let the blood return. When she looked up again Harry was holding out a glass of water, and she drank it thankfully. He shook his head in what might have been admiration and could equally well have been sorrow.

"I never thought I'd say this about the possibility of having a bunch of fanatics pull the wool over my eyes, but by God, Rosalind, you had better be right. If you've misread this, you and I will be responsible for - "

A knock on the door interrupted him, and Lucas entered without waiting for the courtesies. With him was Chen Liu, dishevelled, panting, and wearing an expression that could have been pasted for the purposes of illustration next to any dictionary definition of the word 'panic'.

"Harry, Chen has some information you need to hear straightaway." Lucas looked and sounded perfectly cool and calm, but Ros sensed that he was holding himself in check to help the younger man, who was very obviously neither.

Harry waved them both to seats and gestured to the young Chinese to go ahead. As he always did, Chen looked to Ros for confirmation. She nodded and managed to produce a reassuring smile, which wasn't easy, since her chest was constricted with tension. She used her inhaler, indifferent to the presence of witnesses. After all, Chen was about the only member of the team who didn't know her bloody secret by now.

"Harry, we couldn't tell Pemberton about his son." Chen was still breathless, and the words tripped over themselves in his haste to blurt them out. Ros made a discreet 'slow down' gesture with one hand. "He wasn't there. But the maid – Vicky Leung – she was."

Ros expected Harry to interrupt - his face was set - but he said nothing. His eyes did meet hers for a split second, sufficient for Ros to see her own fears reflected in them.

"She said she'd been worried and she'd wanted to phone me – that is, Constable Tang - but she was afraid."

"Of what?" Harry said quietly.

"That day Alexander Pemberton came to the house he wasn't alone. He said the man he brought with him was a friend, but Vicky – she says she didn't like him. He was almost too polite, stiff – she couldn't really put it into words, sir – well, not in English, anyway. What she said, it would be … well, spooky, I suppose. Sinister, somehow." Chen seemed to realise he was running on, and blew out a deep, steadying breath. "Anyway, she went to make them some tea and he waited for Alex while he showered and changed, but the thing that's bothering her was afterwards. When she was cleaning Sir Roger Pemberton's bedroom. She says she's almost certain someone had been in there – things were 'moved about', she says, and she thinks it was Alex's friend."

"Wouldn't Sir Roger have noticed if a complete stranger had strolled off into his bedroom?" Sceptically, Harry put the question Ros had been about to ask. "Stopped him?"

"He wasn't there, sir. Vicky says he was out at the time so when she went to make the tea this – whoever he was – he was alone."

Harry and Ros exchanged glances, and Ros knew they were thinking the same thing. Because Sir Roger Pemberton had phoned the Home Secretary to inform him that his son had turned up, everyone in Section D had assumed that he was relaying first-hand information. Jesus, Myers. Ros closed her eyes, disgusted with herself. Such a stupid, schoolboy error that could have been avoided by textbook adherence to MI-5's mantra, 'check, check and check again'. If she had, they could have spoken to Vicky Leung long before this.

"Did she say what, specifically, had been 'moved about'?" Harry asked.

"She thought – she was almost sure – that it was a case, a small one, she says – and a largish holdall with parcels in it."

"How can she be sure?" Harry rapped.

She says it's because the pile of the carpet wasn't laying right and there were marks of some kind in the wrong place." Chen clearly wasn't too sure how significant that was, but Ros, from being raised in a succession of diplomatic residences with live-in staff, knew that it was precisely the kind of detail a trained domestic eye would notice. "She was afraid he might have stolen something."

"And she didn't mention this to Sir Roger?"

Chen shook his head. "She said he was angry enough already when she told him Alex had just dropped in and then gone off again. She was frightened he'd take it out on her if anything was missing." Chen hesitated. "You know how it is, Harry – she's an immigrant, low-paid, residence status tied to her job - "

Harry waved him to silence. "And you say Sir Roger isn't there now?"

Chen nodded unhappily."He's away on a business trip, sir." Where he'll have taken the bags. Ros felt sick. "I asked her where, but she doesn't know. Apparently it's hush-hush. Highly confidential. But he'll be back -"

"On Tuesday," Lucas, Harry and Ros said together like a Greek chorus. Fitting, Ros thought savagely. Ruth was the Section's classicist, but she knew enough to be aware that most Greek tragedies were based on the concept of the fatal flaw. In this case the flaw was hers, for carelessly making facile, hasty and incorrect assumptions linking Alex Pemberton's main usefulness to Mahmood and Hamid to his status as a well-known, trusted Olympic insider, when in reality it came from his position as Sir Roger Pemberton's son and the access to his father that they could obtain through him.

Chen pulled his glasses off, rubbed them on his sleeve and peered short-sightedly at Harry. "Yes. I did ask her for a description, Harry. What she said … it was very similar to that Identikit Khalida showed to Samakab Aideed. And the guy was tall."

Just over six feet. Ros wiped her damp hands on her trousers and her fingers crushed the fabric in impotent fury. Take one criminally sloppy piece of intelligence work, one cabal of Machiavellian politicians, add a masterful piece of misdirection and mix well – a recipe for disaster, and now a calamity they might already be too late to prevent.

"Harry?" Callum was peering round the door. "Beckenbridge."

Harry's jaw tightened. "Patch it through. And bring Khalida in here." As Callum disappeared again, he activated the loudspeaker on his desk.

"Mr Beckenbridge, this is Harry Pearce at Thames House. Which hospital is the Home Secretary in?" Ros had barely counted two, and the PPS was still in the middle of his punctillious 'good afternoon' when he continued relentlessly, "He isn't in hospital at all, is he?"

"Mr Pearce, I don't think - " Beckenbridge began. Harry swept on unheeding.

"I'm only too painfully aware of that, Mr Beckenbridge. I also know that your professed concern about leaks doesn't relate to the state of Mr Towers's bladder but to information about a highly sensitive and secret oil agreement with the Saudi government that I believe to be in the final stages of negotiation and signature at this moment at an undisclosed location, probably in or near London." Harry was in full flow now; his voice rang with conviction. "Participants – William Towers, Sir Roger Pemberton, possibly the Foreign Secretary, and various high-ranking officials from the Saudi government and that country's oil industry. Please confirm."

The spluttering and stuttering that emerged from the loudspeaker did, and would have brought a sardonic grin to Ros's face at any other time.

"How do you – that meeting is classified top secret!"

Harry's voice was becoming more menacingly soft with every sentence. "Yes, how curious, you'd think my office would have been made a party to it, wouldn't you? Mr Beckenbridge!" as the politician embarked upon what sounded horribly like a blustering attempt at justification. "I talk, you listen. Carefully. We have intelligence that an explosive device has been smuggled into that location, and that your Minister, your precious oil deal, and your flourishing career are at imminent risk of being blown to pieces along with a sizeable chunk of the leadership of the most expensively-purchased British ally in the Middle East. You may demonstrate the fruits of your creative excuse-writing course on another occasion. Just now I require one simple piece of unembellished information, and if you fail to give it to me you will not only find yourself on the Back Benches once more but possibly also appearing before the Bench in the Old Bailey in the not too distant future. Where is this meeting being held?"


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