Tenison made it sound so straightforward and simple, but in Tartaglia's experience relationships were rarely so cut and dried, nor did they usually end happily on both sides. Either Tenison was naive or he wasn't giving him the full story.

'Did Greville's wife know what was going on with your sister?'

Tenison took a deep breath, as though he found discussing such things unpleasant. 'Some people can't see the nose on their face, but Molly's quite sharp. I'm sure she guessed, although Richard was probably stupid enough, and vain enough, to think he had her fooled. But I don't see her killing Rachel, if that's where you're heading with this.'

'Why's that?'

'What would be the point? The affair was over.' His tone was curt and dismissive.

Tartaglia studied Tenison for a moment. He wondered if his reaction was prudish or merely disapproving. Objectively, he was a good-looking man but there was something flaccid and a little prim about the set of his features that spelled weakness.

'You're sure about that?'

'Positive.'

'I get the impression you don't like Richard Greville very much.'

Tenison shrugged. 'I don't. And I didn't like Rachel getting involved with him, either in business or romantically. But you can't tell people, particularly not someone like Rachel. You have to let them make their own mistakes and hope they learn from them.'

Tenison picked up his glass and got up to refill it, as though he wanted to change the subject.

'So, who has she been seeing since then?' Tartaglia asked, not willing to let it go.

'I really have no idea. I'm sorry,' Tenison said stiffly, over his shoulder, as he mixed his drink.

'She didn't mention anyone to you?'

'Why would she? I wasn't her keeper, and as her brother, I'm probably the last person to know.'

It was a fair point. Thinking about his own love life, or lack of one, Tartaglia nodded. He was hardly likely to unburden himself to Nicoletta; far from it, in fact. Although women were generally more confiding by nature.

Again, he asked Tenison, 'But you are sure the relationship with Richard Greville was over?'

'Absolutely positive,' Tenison said, returning to the sofa with a half full glass and sitting down heavily again. 'I know Rachel. She wouldn't have gone back to Richard, even if he begged her on bended knee and offered her the world.'

Surprised at the strength of Tenison's tone, Tartaglia was struck by the intense look in his eyes. 'Maybe she didn't tell you.'

Tenison shook his head forcefully. 'I knew my sister better than anyone, Inspector. With Rachel, there was no going back.'

It was well past midnight by the time Tartaglia arrived home in Shepherd's Bush. Apart from a ginger cat loping across the road, everything was still, all the windows dark, everybody in bed long ago. He killed the engine and pushed the Ducati up over the icy pavement and into the front garden, careful not to let the gate clang behind him. He parked the bike out of sight behind the high hedge, activated its alarm and covered it with the sheet of plastic that he kept behind the dustbins. His flat was the ground floor of a house in the middle of a small criss-cross of quiet residential streets, close to Hammersmith Broadway. He liked the area, with its wealth of shops and inexpensive restaurants up on the main road, and a couple of good pubs only a few minutes walk away. Convenience was everything when you lived on your own and worked the hours he did.

The solidly built, late Victorian terraced houses were set back from the street behind low walls and strips of front garden. There was something reassuring about their simple redbrick facades and comfortable proportions, with large bay windows on two storeys and attic gables above. Somebody in his family had once said, 'Georgian for beauty, Victorian for comfort,' and he often thought how true that was. Most of the houses in the street had been converted into flats, some owned by the council or local housing trusts, the rest in private hands, with a few still remaining as undivided family homes. Cherry trees lined both sides of the road, their branches now bare and frosted with snow. But in just a few weeks they would be laden with pink blossom, adding a touch of magic to the street.

He opened the front door and, from the small communal hallway, let himself into his flat, straight into the sitting room. He switched on the light and drew the old wooden shutters across the window, blocking out the orange glare of the street lamp immediately outside. They were the original shutters, and when he had first moved into the flat it had taken him days to prise off the layers of paint and get them to work. He had also resurrected as many of the other original features as he was able, taking up the ancient patterned brown carpet, sanding and varnishing the hardwood flooring, stripping the mantelpiece down to its original white marble. He had also unblocked the fireplace, although, when he had first tried to light a fire in the grate, the room had filled with smoke the chimney hadn't been swept for decades.

The central heating had gone off a couple of hours before and the room was cold, with an almost icy chill in the air. He went quickly to the boiler cupboard in the hall and pressed the override button, before going back into the sitting room and removing his jacket. As he undid his tie, he played back the only message on the answer machine. It was from Nicoletta, questioning why he had had to leave so abruptly and asking what he thought of her friend Sarah. It all seemed days ago instead of hours. Perhaps he should have made more of an effort with Sarah. There were moments like this when, tired and alone late at night, he ached for company and for the physical presence and warmth of a woman. But a friend of Nicoletta's was not the answer.

He listened to Nicoletta's voice for a moment, its tone of weary recrimination almost drowned out by the babble of children's voices. When he had had enough, he pressed delete without listening to the rest. Why did she have to take everything so personally? He felt the familiar jolt of irritation, marvelling at how she seemed incapable of understanding the nature of his job or why family lunch shouldn't take precedence over a new murder investigation. Thinking of lunch made him realise suddenly just how hungry he was: he'd survived for most of the day on little more than coffee and a handful of cigarettes. He knew he should get some sleep before the briefing at seven a.m. it was going to be another long day but he had to eat something before going to bed.

He went into the kitchen, opened the cupboards and fridge and took out a small bag of new potatoes, eggs and some parmesan. He saw from the label that the potatoes came from Cyprus, where no doubt spring had already arrived. He washed them quickly and boiled them in their skins before slicing them and frying them in olive oil until they were golden at the edges. As he whisked the eggs and added them to the pan with the grated parmesan, images of the day's events floated through his mind.

He was hopeful after everything Dr Browne had said that the lab would come up with something interesting, possibly even a DNA match. But that was all going to take a while. Meanwhile, establishing a timeline was vital. After what he had heard, it seemed likely that Rachel Tenison had gone running in the park as usual on the Friday morning and possibly met her killer there. But with the assault, if that was what it was, and the killing happening several hours apart, it wasn't straightforward.

When the frittata was nearly done, he browned the top under the grill, then transferred it to a plate, cutting it into wedges and adding salt and pepper and some more parmesan, followed by a large dollop of tomato ketchup. His mother would have thrown up her arms in horror. Tomato ketchup? Marco, how can you? He could practically hear her voice and picture the expression of disgust that went with it. Smiling at the thought, he took his food and a bottle of beer into the sitting room and ate with the plate on his lap.

He finished his meal quickly, put down his plate, and stretched his legs out in front of him, resting his heels lightly on the edge of the coffee table. He lit a cigarette, enjoying the surprising stillness of the hour in the centre of London; only a few weeks ago he had heard a fox barking outside. His thoughts drifted back to the case. Stranger-killings were generally opportunistic, haphazard events, with all the usual hallmarks of a chaotic, sick mind. But the way Rachel Tenison's body had been tied up, almost ritualistically, required careful preparation. Then there was that strange poem. Whatever the killer had meant by it, it was clearly premeditated.

They still had no idea if she had been killed in her flat, or in the park or, indeed, somewhere else, although the more he thought about it, the more the park seemed the most logical place. Removing her clothing made sense. It was the easiest way of destroying forensic evidence, as anyone who had watched CSI a couple of times would know. Again, it showed that the killer was thinking in an organised fashion. But why truss her up like that after death and arrange her in that strange symbolic pose? And why the poem? What message was the killer trying to send? The monochrome image of the naked and bound Rachel Tenison kneeling down in the snow flashed through his mind again. He just couldn't get rid of it. It was odd how, even unbidden, such things imprinted themselves on the memory. Recalling the blandness, the orderliness, the large, scarlet-curtained bed and the weird photographs of her strangely impersonal flat, he wondered what sort of woman she had been. She was an enigma and she intrigued him.

With no easy answers within his grasp and his eyelids starting to feel leaden, he stubbed out his cigarette and forced himself to find his bed, pausing only to remove his clothing before crawling naked under the covers.

4.

It was just past seven in the morning. Donovan manoeuvred her blue VW Golf into a space in the small outdoor car park at the back of the murder squad's offices in Barnes and switched off the ignition. As she climbed out, she noticed how dark the sky was, but at least the snow had stopped for the moment. She was late. Her head still foggy from sleep, she had struggled to wake when the alarm buzzed at six. From where she lived in Hammersmith, it was only a ten-minute drive to Barnes, across the Thames via Hammersmith Bridge. In the summer she would often cycle to work, taking the road that skirted the leafy playing fields of St Paul's Boys' School and ran along the river all the way to Barnes. But in winter, all that mattered was to get to the office as quickly as possible.

The low-built early seventies office block was situated halfway along Station Road, which connected the Green, with its picturesque duck pond and cluster of eighteenth-century houses, to the wilderness of Barnes Common. The brick building was an eyesore in a much sought-after part of town, only a few miles from the centre of London yet with the feel of an old-fashioned village, bounded by the river. The locals were a well-heeled mix of doctors, dentists, lawyers and media types, along with a number of well-known actors, and it was an odd location for two of the Metropolitan Police's murder squads, particularly given the fact that they were rarely ever called upon to investigate a homicide in their own backyard.

A freezing wind gusted around Donovan as she climbed out of the car, whipping the tail of her scarf into her face and stinging her eyes. She slung her heavy bag over her shoulder, gathered her coat tightly around her and rushed through the back door and up the stairs to the first floor.

The morning debrief had just started in the large, open-plan office at the front of the building. The room was crowded and she eased herself onto a desk near the back, beside Nick Minderedes, his thick black hair still wet from the shower, who sat cradling a steaming mug of coffee in his hands. Tartaglia stood at the front of the room, the board behind him already showing a map of the Holland Park area, along with photographs of the victim. Their boss, DCI Carolyn Steele, sat beside him, dressed in her usual uniform of plain dark trouser suit, today's version with a hint of a pin-stripe, plus crisp white shirt. She looked fresh, as though she had managed a full night's sleep, her short, dark hair sleek as usual, her face impassive as she listened to Detective Constable Karen Feeney reporting the findings from several interviews conducted the previous night.

'The park-keeper saw her come into the park just after the gates opened on Friday morning,' Feeney was saying. 'He was sure she was on her own. He said he used to see her most mornings. Apparently, she was often there waiting when he came to open the gates. She always took the same route, he said, which goes right past where her body was found.'

'Did he see anyone else around?' Tartaglia asked.

'No, Sir. But he said it was so cold, he didn't hang around.'

'Well, at least we have our starting point and it's looking more likely that she was killed in the park and left there.' He looked over at Detective Constable Dave Wightman, who was standing at the front of the group, notebook in hand. 'OK, Dave, tell us what you've got.'

Short and thickset, with fair hair, glasses and a boyish face, Wightman was the newest recruit to the team. 'Nothing from local CCTV, so far, Sir,' he said. 'There are no cameras in the immediate vicinity, but we've taken everything from the surrounding area just in case and we're going through it all now.'

'What about the door camera?'

'It's triggered every time someone rings one of the bells, but there's no way of knowing which bell is activating the camera. The footage just shows a continual stream of people coming to the door.'

'How many flats in the building?' Steele asked, in her quiet, flat-toned voice.

'Over forty, Ma'am. It will take a while to eliminate each of the callers.'

'If you need help, you'd better call on the locals,' Tartaglia said. 'Have you tracked down the cleaner?'

Wightman nodded. 'She's a Filipino, lives on one of the council estates in Notting Hill. She was out playing Mah Jong all night and I've only just managed to speak to her now. She said she cleaned for Rachel Tenison on Tuesdays and Fridays and has worked for her for just over two years. Last Friday she arrived as usual around ten o'clock. When she let herself in, Miss Tenison's handbag was in the hall, which she said was odd, and the flat was unlocked and the alarm was off, which also wasn't normal. She thought Miss Tenison was at home until she realised there was nobody there.'

'Maybe Rachel Tenison didn't bother with the alarm when she went out for a run. If so, it means she never returned to the flat after the run.'

'The cleaner didn't say, Sir. Miss Tenison was never at home when she came in to clean. They usually spoke on the phone or left each other notes.'

'Was anything else out of the ordinary?' Steele asked.

'She thought not, Ma'am.'

'So, what sort of state did she find the flat in?' Tartaglia asked. 'Was it a mess, was it tidy, untidy?'

'Said it was quite tidy, or at least I think that's what she said.' Wightman consulted his notes then added, 'Nothing that aroused any suspicion, at any rate.'

'Had the bed been slept in?'

'Yes.'

'But nothing unusual?'

'No, Sir. She said she cleared away some glasses and a couple of empty wine bottles.'

'Where were they?'

Wightman again checked his notes. 'In the sitting room. She said it looked as though Rachel Tenison had had guests. She said she put four or five glasses in the dishwasher but she didn't set it off because it was more or less empty. She said Miss Tenison liked to fill it up before switching it on. Something about saving electricity.'

'The glasses have gone off to the lab,' Tartaglia said, addressing the room. 'At least we now know when they were used.'

'Perhaps some of the glasses were there since before Thursday night,' Steele said.

Tartaglia shook his head. 'From what I've seen, Rachel Tenison doesn't seem like the sort of person to leave dirty glasses lying around for days.'

Wightman nodded. 'The cleaner said she liked things nice and tidy, that there was never much of a mess to clear up, unlike some of her other jobs. Said it was a pleasure to work for her.'

Tartaglia rubbed his chin thoughtfully. 'So, let's assume the glasses were from Thursday night. Rachel Tenison went out running early Friday morning. She probably intended to clear them away when she got back. What about her running clothes? Did you ask the maid if she found them in the flat?'

'There was a basket of dirty clothes, which she washed, but they were all dry. It was snowing heavily Friday morning. If Rachel Tenison had been out running, her clothes would have still been sopping at ten o'clock.'

'Yes. So it's looking more and more as though Rachel Tenison never went back to the flat to change. Thank God the dishwasher was nearly empty and we have the glasses. At the moment they're the only things we have to go on.' He looked over at Nina Turner, who had just come into the room. 'What's the latest from the park?'

'No sign of her clothing or personal possessions yet, but hopefully something will turn up today.'

She was looking even thinner and more angular than usual in a plain grey trouser suit and blue shirt that highlighted her olive skin. Her long dark hair was tied back in a ponytail and she was fully made up even at that early hour of the morning, something that Donovan wasn't sure whether to admire or despise.

'How long do you expect to keep the park closed?' Steele asked.

'Another couple of days,' Nina replied, with a glance in Tartaglia's direction. 'Progress is slow with all the snow. At least we now know where she entered the park and which route she is likely to have taken. We had the dog teams in yesterday, and they'll be back again today. We'll keep looking, but to be honest, apart from her clothing and personal things, I don't hold out much hope. Assuming she was killed on Friday, the park was open for business for two whole days before we sealed it off.'

'What about the victim's flat?' Tartaglia asked.

'We finished the powdering last night and removed a number of prints which have gone off to the lab.'

'And her things?'

'We'll be going through everything today. When we're finished, we'll start on the luminol spraying.'

Tartaglia looked over at Minderedes. 'What have you got, Nick?'

Minderedes slid slowly off the desk, mug in hand, and cleared his throat. 'Uniform are trying to trace any runners or dog walkers who might have been in the park that morning, but so far the few that have come forward all say they were there later. Nobody saw anything amiss.'

'You've told CID to run background checks on all of them?'

Minderedes nodded.

'So her body was either well hidden by then, probably in the thicket where she was found, or it had been taken somewhere else, although that seems unlikely.'

'Maybe she met her killer in the park and went off with them somewhere, where she was killed,' Minderedes said. 'The killer then came back and dumped her body in the park later.'

Steele shook her head. 'Possible, but unlikely. If the killer came across her in the park, why take her away somewhere and then bring the body back? We're talking central London here, not some deserted woodland. That park is crawling with people during the day. It's too risky.'

'I agree,' Tartaglia replied. 'And as we now know, her body was found very close to her usual running route. Let's stick with the most obvious explanation for the moment, unless something new comes to light.'

'But she was assaulted several hours before she died,' Karen Feeney said, from her desk at the front. 'How does that tie in?

Tartaglia nodded. 'All we know is that she had sex with somebody a few hours before she was killed very rough sex, by the sounds of it. She also had quite deep abrasions on her wrists and ankles where she had been secured. But it might have been consensual. We know nothing yet about her personality or background.'

'So what do you think happened?' Steele asked. 'Some sort of sex game gone wrong, perhaps?'

'Quite possibly, although the killer may not be the person she had sex with. Rachel Tenison went running most mornings, so maybe someone's been watching her or maybe it's somebody she already knows.'

'Was she gay or bi-sexual?'

'Not according to her brother, but obviously it's something we must check as we go along. A woman could easily kill another woman with an arm lock, if she knew what she was doing. We mustn't rule out a woman having done this, although as you all know the statistics are against a woman committing this sort of crime, particularly given the potential sexual motivation.'

'But why use an arm lock?' Feeney asked. 'Surely, the killer would come at her from the front and strangle her with his hands.'

'It's possible the victim tried to get away,' he said. 'Maybe the killer only intended to subdue her. It's easy to go too far, for things to get out of control in the heat of the moment. Anyway, as the victim struggles to free herself, something the killer's wearing maybe a watch or a bracelet or something sharp like that, cuts into her, under her chin. All of this could have taken a matter of minutes, at the most. At some later point, the body was moved. Hypostasis indicates that she was lying flat on her back for several hours before she was tied up again. Maybe the killer was disturbed and had to go back later to finish the job, to make a spectacle of her. The killer strips her naked, ties her up with duct tape and puts a poem in her mouth, then arranges the body in a kneeling position, almost sacrificial. You've all seen the photos by now.'

'She looks like she's praying,' Feeney said.

'Begging for mercy, more like,' Minderedes added.

Tartaglia nodded. 'It's a deliberate message of some kind, although it's open to interpretation.'

'We were really lucky to find her so quickly,' Donovan said, thinking back to the overgrown enclosure in the woods. 'She could have been there weeks, if not months. The kids who discovered her were only able to get inside because part of the fence had come down and there had been no time to repair it.'

'That's right,' Tartaglia replied. 'We have to assume that we weren't meant to find her so quickly. We're looking at a killer who's organised and thinking clearly, not someone in a panic. That's as much as we can tell at the moment. In the meantime, we must concentrate on the victim profile and find out who Rachel Tenison saw on the Thursday night after she left work. Have you got hold of a copy of her diary yet, Nick?'