Surprised, Sherlock groped in the inside pocket of his coat. 'I have it right here.' But his fingers came back empty.

Mycroft's expression, expectant for an instant, reformed itself into anger. 'For goodness sake, Sherlock. Again? Don't you ever think, or are you too busy making gooey eyes at her to ask about her motivations?'

Sherlock felt his forehead crease as he tried to follow Mycroft's reasoning. He could easily have lost the USB stick while walking along the street, or dropped it coming up the stairs, there wasn't an automatic connection to Irene as Mycroft was suggesting – or if there was he'd missed it.

His brother rose from the chair, paced the carpet in front of the fire, pausing to kick library books out of the way with unwonted violence.

'I will tell you what really happened in Karachi, shall I, and this was after you'd finished riding to the rescue on your white charger. It came to my attention that a British national had been beheaded, although the photographic evidence provided by the terrorists was quite convincing, there was no video to back it up. I investigated. I found the flight records of Yuri Gregarovitch, a prominent Russian assassin, who flew out of Karachi airport only a few hours after Miss Adler's purported death. I interrogated the terror cell, who readily volunteered that fact that she had been rescued by a man speaking Russian. I located the storage container hired in a Russian name. I tested the blood, the handcuffs, the hair samples, the clothing on the deck rail and concluded that Miss Adler was probably dead, and if not dead, then captured by our erstwhile allies.

And what do you think I did then, little brother? What do you think I did? I may not be able to read every scintilla of emotion that flies through your vapid head like Doctor Watson here, but to my extreme disappointment, we are still related. I extracted vengeance. She was one of ours, after all, but I confess I wasn't really doing it for her. I put pressure on my Russian counterparts to bring Yuri Gregarovitch to justice. When they wouldn't, I imposed sanctions – oh, I persuaded the UN to do it for a different reason but the murder of Miss Adler was my main motivation.

In the end Gregarovitch's body was found floating face down in a river in Moscow. They were forced to eliminate one of their best agents because of a deception that you put together and that I mistakenly believed. They've been looking for a way to get revenge on me ever since.'

He wheeled around. 'Doctor Watson. Are you familiar with the concept of a honey trap?'

John nodded, 'It's where someone is paid to put someone else in a compromising position.'

'Exactly. It's where a woman convinces a man to have sex with her to either blackmail him or in this case, to get him to do what she wants. My brother already has a history of taking this kind of bait.'

Sherlock was stung into a response, glaring across the room. 'That's not what happened. This was different.'

'Sherlock,' replied Mycroft silkily. 'Where is your phone?'

Sherlock removed it from his coat pocket, tapped it back to life. 'She didn't take it, I would have noticed. And anyway, this can't be related to your missing treaty, she sent me the key to the puzzle box two and a half years ago, whereas you only lost it in the last two months.'

The mobile was snatched from his hand.

'You make the mistake, once again, of thinking that the whole world revolves around you.' Mycroft drew out his own phone. 'Ah, here we are, right on cue.'

He tapped the screen once, and Irene's voice came rushing out of the tiny speakers, scratchy and coarse. 'I want your attention,' she said. 'While you are here I want your conversation, I want your trust and I want you to be honest with me. But most of all, I want to watch you when ...'

'Turn it off,' Sherlock yelled, drowning out the rest of the sentence.

He barrelled off the settee, attempted to snatch the offending device out of his brother's hand, and stop the betrayal being played out on it.

'I'm afraid not.' Mycroft regarded him with something approaching sympathy, which sent a wave of sickness burning through his guts. 'I need to see what sort of trouble I'm in.'

John spoke, covering the next few lines of dialogue. 'That's her, I know that voice. Who's she talking to? Let me see the screen, Mycroft.'

A series of very distinctive noses filled the room as John wrestled for control of the mobile. Unzipping noises. Sucking noises. Sherlock walked out.

The pain that shot through him was almost as strong as the emotion that had led him to her flat in the first place. He'd thought his heart was unassailable, but this hurt was like someone had prised it out of its box and was slicing it into pieces as he watched. He made it to the bottom of the stairs, attempted to leave the flat in search of something, anything, he wasn't quite sure what, but the booted thugs with whom his brother had arrived were blockading the alley and he couldn't get out.

Back upstairs the very private, very personal sounds he'd made while in her arms boomed around the flat. Mycroft had turned up the volume.

Sherlock shucked off his coat and jacket, rolled up his sleeves and sought the sanctuary of his study. Over the last six months he'd constructed an intricate distillery to purify and refine his most preferred methods of escape with into an easily injectable form. Someone had already taken the latest batch of finished products though; the room still glittered its crystal promise but it could no longer provide him with the oblivion he needed.

Slowly he picked up a glass beaker, hefted it a few times, then threw it at the wall. The next phial followed, and the next, and the next until the floor sparkled and everything was smashed.

He was still sitting amidst the ruins when John pushed the door open a few minutes later, surveyed the room carefully, then crouched on the floor in the next space along.

'Irene recorded the whole night,' he said, and Sherlock could hear the effort his friend was making to remain calm. 'In the first bit of video the light is on, to confirm the fact that it's definitely you, I would think. Then she turns the light off and opens the curtains and you fall asleep. She goes through your clothes, takes out your phone and leaves the room with it. Then she comes back in, walks over to the camera and switches it off. It was a set-up, she knew what she was doing. I'm so sorry.'

From the living room, Sherlock could hear his own voice. 'I love you,' he said, then there was a blur of noise as Mycroft spooled the recording back. 'I love you. I love you.'

He raised a hand and let it fall. 'He's right. In the morning, I couldn't find my phone and then in the alley outside I was barged by a man. I expect he was putting the phone back in my pocket, complete with whatever tracking software they'd installed. Today, I texted Mycroft to say I'd found the treaty and then, on the way here I was pickpocketed again, the same man again I think, although I wasn't paying much attention. They've been incepting my messages, they knew exactly where I was.'

He shook his head, resigned. 'She didn't want me, she just wanted my phone. This is revenge.'

'But you saved her life, didn't you?'

'I was the one who put it danger in the first place. She's never forgotten that. Or forgiven it.'

In the living room Mycroft's mobile was ringing, and fell silent as his brother held a muttered conversation. After a short while, Mycroft's shoes tapped down the corridor and he pushed open the study door.

'The video has been sent to senior members of the Cabinet and the security services along with a message thanking you for your help in passing secret information to the Kremlin. Our government is demanding decisive action from me, since I am responsible for the security breach. I have had to accede to their demands. If it helps you at all brother, this isn't personal, it's me that Moscow is interested in removing, you are simply collateral damage. I'm afraid that this time, I really am going to have to send you away.'

'More suicide missions, Mycroft?' John queried. 'Don't you have any better ideas?'

'Actually, the solution this time is rather more final.' Mycroft sighed. 'And suggested by my cold war counterparts. They want you locked up.'

He nodded in confirmation of Sherlock's unspoken question. 'It will cut down on my travel expenses having two siblings in there, at least.'

There was a noise from Mycroft's pocket, the throaty cry of a person reaching physical climax, although where once the text alert had been Irene's voice, now the exhalation was Sherlock's own. With a grimace, Mycroft retrieved it, read the message. 'Goodbye, Mr Holmes.'

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