'Fucking get back, Simon,' Tartaglia shouted.

Without warning, Jennings lunged at Tartaglia, thrusting the knife towards his chest. Moving fast, Tartaglia turned with a scissor movement, grabbing hold of Jennings's knife hand and slicing his other arm down hard on Jennings's elbow. He heard the snap of bone. Jennings screamed and the knife clattered to the ground as Tartaglia forced him down onto his face on the floor.

'Cuff him, will you, Simon?' Tartaglia said, kicking the knife away into a far corner, as he held Jennings down.

Before Turner had a chance, Minderedes appeared through the doorway, ready with a set of cuffs, and bent over Jennings.

'I'll have you for this,' Jennings yelled at Tartaglia. 'I'll fucking have you for this.'

'Shut it or I'll hurt you even more,' Minderedes growled. Securing Jennings, he pulled him to his feet, still yelping with pain, and turned to Tartaglia. 'There's a couple of uniforms waiting outside, Sir. We'll take him to the local nick and get him a doctor.'

'His arm's broken. You'd better get him straight over to A&E. But whatever you do, don't take off the cuffs. He's desperate to get away for some reason.'

'Jeez, Mark. You're lethal,' Turner said, wiping the sweat from his brow with his hand as Minderedes propelled Jennings out of the room. 'Didn't know we had fucking Steven Seagal on the team.'

'It's ju-jitsu, not aikido,' Tartaglia replied sharply, wanting to put him in his place. Maybe it was nerves on Turner's part and the release of tension, but it didn't feel right to make light of things. He wasn't proud of what he had done, but it was either that or take a knife in the chest and, in his view, Turner had provoked the whole situation unnecessarily.

'Bloody useful, whatever it was,' Turner said, nodding slowly as though it meant something to him. 'You a black belt, or something? Maybe you can teach me a few moves.'

Tartaglia said nothing.

'When did you learn all that stuff?' Turner persisted, trailing him out of the room.

'At school. I don't practise it now.' It was over fifteen years since he had last set foot in a dojo, but it was one of those things, like riding a bike, which you never forgot; instincts and reactions still as natural as breathing and automatic. Luckily, he rarely ever had cause to use it.

'You like the tough guy stuff?'

'Quite the opposite. I was being bullied.'

'What, you?'

'It can happen to anyone. My dad thought martial arts would give me confidence.'

'Is that what did it?' Turner said with a half smile. 'There was I thinking it was the Latin blood.'

Resisting the urge to wipe the silly expression off Turner's face, he stopped outside the bedroom door. 'I just want to check on Heather.'

He pushed open the door and went inside. She hadn't moved. He knelt down beside her and listened again for the sound of her breathing. He could barely hear anything now. She was cold to the touch and for a moment he couldn't find her pulse. He put his face close to hers again. There was no smell of alcohol on her breath as far as he could tell, which was good, although it was possible she had taken a cocktail of something else with the heroin. Maybe she would be OK; maybe she would wake up on her own. But instinct told him she was slipping away. Apart from the human cost of a girl he had never spoken to, to whom he felt some peculiar bond due to her resemblance to Donovan, they could not afford to lose her. She was the only person alive that they knew of who could bear witness to the perverted character of Michael Jennings.

'Turner!' he shouted urgently, not taking his eyes off Heather.

Turner put his head around the door. 'She OK?'

'No. Get a fucking ambulance.'

29.

'I didn't do it. I had nothing to do with Dr Watson's murder. How many times do I have to say it for you to believe me?' Eyes tearing, hands clasped in front of him, Michael Jennings looked imploringly across the table, first at Donovan and then at DS Jason Pindar, next to her.

Donovan shook her head slowly from side to side as though she had seen it all before and didn't believe a word of it.

They were in a room at Camberwell Police Station. It was nearly eight in the evening and the tape and camera had been running for almost two hours. Tartaglia, Steele and Turner were sitting in another room nearby, following the proceedings on video link. Tartaglia was watching Jennings's every reaction to the questions put to him, but his boyish face remained a picture of unwavering innocence, the heavy-duty plaster on his arm and the sling an additional, theatrical touch of helplessness. With his mop of blond hair, snub nose and blue eyes, he appeared incapable of doing anything nasty more likely to be rescuing a cat stuck up a tree or helping old ladies across the road than committing violent acts of rape, torture and murder. Hunched low in his chair, with his torn, paint-spattered jeans, fleece and dirty trainers, he looked like any young student. It was almost impossible to imagine that this man had pulled a knife on him and Turner several hours earlier.

Jennings's brief, Andrew Harrison, was a tall, angular man in an ill-fitting suit, with a shock of greasy black hair and heavy-framed glasses. He sat beside Jennings, fiddling with the top of his pen and, for the most part, he let Jennings deal with the questions on his own. Jennings was doing well without him, and Donovan and Pindar were finding it impossible to make any headway. Whatever they threw at him, he just hit it straight back. He was innocent of Watson's murder and nothing would make him say anything different.

It looked as though they were in for a long night and Tartaglia wondered how he was going to endure it. The small room was stiflingly hot and airless, the atmosphere so dry his throat felt raw. He and Turner had taken off their jackets and ties and rolled up their sleeves, but it made no difference. The sweat was running down his neck and his shirt felt constrictingly tight across his chest and shoulders as though it had suddenly shrunk. He could smell Steele's faint lemony perfume, though it was almost smothered by the acrid odour of cigarette smoke that hung around Turner like a cloud. Turner had already nipped out once on some pretext and had come back reeking of it. Tartaglia was surprised Steele hadn't noticed, but her nose was blocked, judging by her thick nasal tone. She sat next to him, even paler than usual and shivering, her overcoat wrapped tightly around her shoulders like a blanket and an ice blue woollen scarf wound several times around her neck. She had a large bottle of mineral water beside her, which she sipped from sporadically, and had insisted that the window remained closed.

'Jennings is good, isn't he?' Turner said, glancing round at Tartaglia and Steele. 'This is exactly the sort of stuff he gave us last time round. You'd think butter wouldn't melt. We went over and over everything but he kept singing the same effing tune.'

'I guess if the wheel ain't broke, why fix it?' Tartaglia said, thinking back again to the very different Jennings he had faced earlier, the one with real madness in his eyes. If only that had been captured on film, to replay to a jury or whoever was going to be investigating Jennings's complaint about the way he had been arrested and the injury he had received.

'He's a real little boy scout,' Turner replied acidly. 'Put him in a suit and tie and tidy him up a bit and any female member of a jury's either going to want to mother him or shag him.'

'It's never going to get that far, at this rate,' Steele said with feeling, turning bleary, red-rimmed eyes briefly on Tartaglia and Turner. She gave a dry hacking cough, took a pack of tissues from her bag and blew her nose loudly. 'I don't see Jennings confessing to anything. We're going to have to find something else.'

'I 'ave your signed statement here, from when you was last interviewed,' Pindar continued, in his deep, flat tone. 'You said you never met Catherine Watson outside university. You said you had never been near her home. Yet we turn up these photos of the pair of you, taken two days before she died. There's you and Watson, in a caff five minutes from her house. You're even sitting at the same table.'

'I tell you, I didn't know where she lived,' Jennings said, his voice rising. 'I must have bumped into her. That's what must have happened.'

'Doesn't look that way to me. You're waiting for her when she comes in. She goes right over to where you are and sits down, like she's expecting to see you. What do you make of that?'

'I just happened to be there. It was an accident.'

'But you didn't live anywhere near there,' Donovan said insistently. 'Why did you go to that particular cafe?'

'I don't remember.'

'You had an arrangement to meet there, didn't you?'

'No.'

'Then why go there? Why choose that cafe? '

Jennings shrugged. 'Maybe someone had told me about it. Maybe it was Dr Watson, but I just don't remember. I'm really sorry.'

'That's a lie and you know it.'

'No,' Jennings shouted, gripping the edge of the table with his good hand. 'I'm not lying. It's God's truth.'

'You're full of shit,' Donovan said, with a dismissive shake of her head.

'Why won't you believe me?'

'OK, Mr Jennings,' Pindar continued, more quietly. 'Let's say for a minute, we believe your little story. Why didn't you tell us about it before?'

Tartaglia saw a flicker of relief on Jennings's face, or possibly a glimmer of hope as though Pindar had offered him a lifeline.

'I'm sorry I forgot to mention it,' Jennings said. 'Honest I am. It must have slipped my mind.'

'Slipped your mind?' Donovan's tone was incredulous. 'You are joking.'

'Look. I was upset when I heard what had happened to Dr Watson. Incredibly upset. I just plain forgot.' He looked at her beseechingly, willing her to believe him. 'I'm telling the truth. Please will you listen.'

Donovan shook her head. 'I don't buy that, Michael. It was just two days before she was murdered. How could you forget such a thing so easily?'

'I told you, I was very upset. Anyway, we just had a coffee, that's all. No big deal. I didn't think any more about it.'

'So you met by chance? You really expect us to believe that?'

'But it's the truth. What more can I say?'

'How do you explain following her home?' Pindar shoved a sheaf of photographs across the table. 'For the benefit of the tape, I am showing Mr Jennings photographs taken in the Finchley Road and West End Lane, on Thursday, ninth of February 2006, between three twenty-four p.m. and four thirty-seven p.m.'

As Pindar laid the photographs out in sequence on the table, Donovan leaned forwards across the table towards Jennings. 'They show you, Mr Jennings, following Catherine Watson out of the cafe and along the road.'

With a cursory glance at them, Andrew Harrison gave a small cough. 'With all due respect, they don't show that at all.'

'You then follow her home,' Donovan said, ignoring the solicitor.

Jennings squinted short-sightedly at the photographs and shook his head. 'Is that really me?'

'The fact that my client and Dr Watson appear in the same photographs means absolutely nothing,' Harrison said, with a shrug of his narrow shoulders.

'Are you sure that's me?' Jennings was still studying the photographs with a look of deep puzzlement that Tartaglia found disturbingly convincing.

Jennings was playing his part to perfection, as good as any seasoned actor from the Royal Shakespeare Company. He thought back to the Jennings he had seen in Heather's flat and the raw panic and anger in his eyes. He hadn't been faking then. That was the real Jennings.

'You saying it's not?' Donovan asked.

'If it is, it was a coincidence. I mean, I may have been going the same way, but I wasn't following her.'

'That's rubbish and you know it.'

Harrison shook his head. 'These are busy streets, Sergeant. We're hardly in the back of beyond. The fact that my client appears to be taking the same route as the victim can be interpreted many ways. There are lots of other people in the photographs.'

'But they didn't all know Catherine Watson, did they?' Donovan replied.

Pindar cleared his throat. 'The last few photographs show Mr Jennings at the bus stop outside Catherine Watson's house.'

'You followed her home because you were obsessed with her,' Donovan said, locking eyes with Jennings. 'Isn't that right?'

'No. I liked her, of course. She was my tutor and she was a nice woman. But it wasn't anything more than that. I wasn't obsessed with her.'

'What were you doing at the bus stop outside her house?'

'Catching a bus, I imagine.'

'Where were you going?'

'I have no idea. Home probably.'

'You were living where at the time?'

'Kennington, I think. Or maybe Clapham. I can't remember.'

'According to your statement, it was Clapham.'

'If you say so. I moved around a lot. Couldn't find anywhere decent that I could afford.'

'None of the buses from her street go anywhere near Clapham.'

'Maybe I thought I could change or catch a tube. I honestly don't remember. I mean, can you remember what you were doing on a particular day two years ago? Can you?'

'We're the ones asking the questions, Mr Jennings.'

'But it's a fair question, isn't it?' Jennings turned to Harrison. 'I'll bet they can't.'

'Yes,' Harrison said. 'It's a very fair question. I'm sure a lot of people will agree with you.'

'Going back to the photographs-'

'Excuse me, Sergeant. But all you've come up with so far is a set of old photographs that don't add up to anything. Unless you've got something else up your sleeve, I suggest we call it a day right now.'

'We'll sit here all night if need be.'

'You'll be wasting your time. Based on what you've got here,' he said, tapping the table, 'you haven't got any prospect whatsoever of charging my client with murder and you know it.'

'Your client is going nowhere, Mr Harrison. We know he murdered Catherine Watson.'

Jennings cleared his throat. 'Excuse me, but if you're going to keep me, please can we take a break?' He put his one good hand on the arm of his chair and half rose. 'I'm really sorry but I need the toilet.'

With a glance at Pindar, Donovan nodded. 'OK. Let's take a ten-minute break here. Interview suspended at eight-fifty p.m.'

'I think I'll follow suit,' Turner said, getting to his feet and cracking his knuckles loudly one by one. He had the edgy look of a man wanting a cigarette rather than a pee, but Tartaglia said nothing. He felt deflated. If Jennings carried on with this show, and there was no reason to think he would crack, they had nothing.

'One minute, Simon,' Steele said, making an effort to push back her chair so that she could see both him and Tartaglia. 'If Jennings killed Catherine Watson, he's the best bloody actor I've come across in years. Am I missing something? We're sure he's our man?'

'He's a clever sod,' Turner said wearily, wiping the sweat from his brow with his hand, as he loomed large over both of them. 'In the absence of anyone else, I suppose he's our best bet.'

Shaking his head, Tartaglia stood up. 'He's more than that. Much more than that. I'm convinced now that he murdered Catherine Watson. When I saw what he'd done to Heather, his girlfriend, any doubts I had went out the window. The marks were almost identical to the ones on Catherine Watson's body. He also threatened to kill Heather if she gave him away and I believe he meant it. You said she was really terrified.' He looked at Turner. 'Simon?'