'Well?' she demanded as they rode the lift back to the ground floor.

'Henderson gets off shift at nine-thirty. Nine-fifty she's on camera, changed and ready to go home. Ten-thirty she's back in her uniform again, leaving the building.' Watson opened her mouth, but Logan carried on, grim triumph in his voice. 'We were looking for someone covered in blood. Mrs Henderson just got changed and walked right out of there as if nothing ever happened.' They grabbed a pair of uniformed officers from the search party and called back to base. DI Insch was not in the best of moods when the call was put through: he sounded as if someone had been massaging his backside with red-hot pokers. 'Where the hell have you been?'he demanded, before Logan could get a word in. 'I've been trying to call you for the last hour!'

'Still at the hospital, sir. All mobile phones have to be switched off…' But mostly he'd switched it off so Colin Miller couldn't call him back.

'Never mind that! Another kid's gone missing!'

Logan felt his heart sink. 'Oh no…'

'Aye. I want you to get your arse over here to Duthie Park: the Winter Gardens. I'm pulling in all the search teams. Bloody weather's getting worse, snow's going to make any evidence we've got disappear. This is now our number one priority!'

'Sir, I'm just on my way to arrest Nurse Michelle Henderson-'

'Who?'

'Lorna Henderson's mother. The kid we found in Roadkill's steading. She was at the hospital last night. She blames Roadkill for her daughter's death and the break-up of her marriage. Motive and opportunity. The Fiscal agrees: apprehension and search warrants.'

There was a moment's silence on the other end of the phone, then a muffled conversation as Insch gave someone else a hard time. And then the inspector was back. 'OK,' he said, sounding as if he was about to clobber someone. 'Pick her up, chuck her in a cell and get your backside over here. Roadkill's not getting any more dead. This kid might still be alive.' They stood on the top step in the snow while Logan rang the doorbell again. 'Greensleeves' started up for the fourth time.

Watson asked Logan if he wanted her to kick it down, her breath fogging in the chilly air, nose and cheeks bright red. Behind them the two uniforms they'd liberated from the hospital search team expressed their agreement. Anything to get out of the freezing cold.

He was just about to give her the nod when the door opened a crack and Nurse Michelle Henderson's face appeared. Her hair looked like a chimpanzee had slept in it.

'Can I help you?' she asked, the chain still on the door. Her words reeked of stale gin.

'Open up, Mrs Henderson.' Logan held up his warrant card. 'You remember us. We need to talk to you about what happened last night.'

She bit her lip and looked at the four of them, standing there like carrion crows against the falling snow. 'No,' she said. 'I can't. I have to get ready for work.'

She went to close the door, but WPC Watson already had her boot wedged into the thin gap. 'Open up or I'll break it down.'

Mrs Henderson looked alarmed. 'You can't do that!' she said, clutching the neck of her dressing gown closed.

Logan nodded and pulled a thin sheaf of paper from his inside pocket. 'We can. But we don't have to. Open up.'

She let them in.

It was like stepping into an oven. Michelle Henderson's little flat was a lot tidier than it had been the last time they were here. Everything was dusted, the carpet hoovered, even the Cosmopolitans on the coffee table had been stacked in a neat pile. She sank into one of the lumpy brown armchairs, drawing her knees up under her chin, like a small child. It made her bathrobe fall open and when Logan sat on the sofa he took care not to avail himself of the view.

'You know why we're here, don't you, Michelle?' he said.

She wouldn't look him in the eye.

Logan let the silence grow.

'I…I have to get ready for work,' she said, but made no move to get up, just hugged her knees all the tighter.

'What did you do with the weapon, Mrs Henderson?'

'If I'm late then Margaret can't get away. She has a toddler to pick up from nursery. I can't be late…'

Logan gave the nod and the pair of PCs left the lounge to give the house a quick once-over.

'You got blood all over your clothes, didn't you?'

She flinched, but didn't say anything.

'Did you plan it?' Logan asked. 'Make him pay for what he did to your daughter?'

More silence.

'We've got you on tape, Mrs Henderson.'

She stared hard at a spot on the carpet that had somehow eluded the hoover.

'Sir?'

Logan looked up to see one of the PCs standing in the doorway clutching a mound of blanched clothes. There was a pair of jeans, a T-shirt, rugby shirt, two socks and a pair of trainers all bleached almost white.

'Found these hanging over a radiator in the kitchen. They're still damp.'

'Mrs Henderson?'

No response.

Logan sighed. 'Michelle Henderson, I'm arresting you for the murder of one Bernard Duncan Philips.' Duthie Park was a well-manicured stretch of parkland on the banks of the River Dee, complete with duck pond, bandstand and fake Cleopatra's Needle. It was a favourite spot for families, its wide-open spaces and ranks of mature trees giving plenty of scope for children to play. Even buried under a foot of crisp white snow there were signs of life. Snowmen in various stages of construction punctuated the white plain like standing stones: silent watchmen, lords of all they surveyed.

Jamie McCreath – four in two weeks' time, the day before Christmas Eve – had disappeared. He'd been on a trip to the park with his mother, a distraught woman in her mid-twenties with long red hair the colour of autumn leaves escaping from under a knitted hat with a ridiculous gold tassel on top. She cried on a bench in the Winter Gardens while a flustered-looking woman with a small child in a pushchair did her best to comfort her.

The Winter Gardens – a large Victorian structure, white-painted steel holding up tons of glass, protecting the cactus and palm trees from the snow and ice outside – were a hive of activity, crawling with uniformed police officers.

Logan found DI Insch standing on an arched wooden bridge spanning a blue, dappled pool full of gold-and-copper fish. 'Sir?'

The inspector glanced over his shoulder, a frown sitting on his round features, making him look bullish and impotent. 'You took your bloody time.'

Logan tried not to rise to the bait. 'Mrs Henderson's keeping her mouth shut. But we found all the clothes she was wearing drying on the radiator. Every last one of them bleached within an inch of their lives.'

'IB?' asked Insch.

'I've got them going over the washing machine and the kitchen. Those clothes must have been saturated with blood. We'll find it.'

The inspector nodded, lost in thought. 'At least that's something,' he said at last. 'I've had a call from the Chief Constable: this is the last kid that goes missing. Four of Lothian and Borders finest are on their way up the road as we speak.'

Logan groaned. That was all they needed.

'Aye,' said Insch. 'Show the poor thick parochial bobbies how to do it properly.'

'What happened?'

The inspector shrugged. 'Too much publicity, too little progress.'

'No, here-' Logan indicated the verdant jungle sprawling under glass all around them. 'What happened with the kid?'

'Ah. Right.' He straightened up and pointed towards the entrance, hidden behind a large clump of tropical rainforest. 'Mother and child enter the Winter Gardens at eleven fifty-five. Jamie McCreath likes the fishies, but the birdies frighten him. Aye, and so does that bloody talking cactus. So they come in here and he sits on the edge of the bridge and watches the fishies swimming about. Mrs McCreath spots a friend and says hello. They talk for a while, about fifteen minutes she thinks, and next thing she knows Jamie is nowhere to be seen. So she starts looking for him.' He held out a large hand and traced it along the paths that crossed and bordered the pond. 'No sign. She's seen the papers and the telly, so she starts to panic. Screams the place down. Her friend calls 999 on her mobile, and here we are.' He let the hand fall back to his side. 'We've got four search teams going through the place: under every bush, bridge, into every storeroom. You name it. Another two teams are out in that-' Insch inclined his head towards the fogged up glass, indicating the park outside. 'We'll get more teams doing the park when they arrive.' Logan nodded. 'What do you think?' Insch slowly sank forward, his elbows on the railings that bordered the wooden bridge, his face closed, staring down at the fish swimming languidly below. 'I'd love to think he's just wandered off, bored. That he's outside building a snowman…But deep down? I think he's got him.' He sighed. 'And he's going to kill him.'