Erika and McGorry came back to the police support van, where a group of six officers were taking a quick break. They had been chatting away, but fell silent when they saw Erika.

‘Don’t mind me,’ she said.

‘Refreshments have arrived, ma’am,’ said one of the officers, indicating the table in the corner with an urn and a cluster of pre-packaged sandwiches.

‘Thanks. What’s your name?’ she asked.

‘PC Rich Skevington, ma’am.’

Erika and McGorry grabbed a sandwich each and filled paper cups with steaming coffee. The sound of the coffee hitting the paper cup was loud in the silence. Erika looked around. She didn’t recognise any of them; they all seemed so young.

‘Who can give me an update on the house-to-house?’ she asked, ripping the plastic off her sandwich and taking a bite.

‘We haven’t been able to get an answer from Don Walpole and Ivan Stowalski. We’re waiting on their mobile phone numbers,’ said Kay, the young officer who’d lent Erika her shoes.

‘What about the rest of the street? Are people being helpful?’ asked Erika, washing down a mouthful of the dry sandwich with a gulp of coffee.

‘Half the houses are empty, but the locals who knew Marissa Lewis also knew about the affair she had with Don Walpole and that she was sleeping with Ivan Stowalski behind his wife’s back.’

‘The jury’s out as to whether or not Ivan Stowalski’s wife has left him,’ said Rich. ‘Their next-door neighbour, a beady-eyed old girl, says they’re both up north for Christmas visiting his family. We’ve also been on the lookout in gardens and dustbins for the victim’s mobile phone, in case it’s been dumped, but nothing so far.’

‘How are the team getting on over at the Estate?’

‘I’ve just come back,’ said another young male officer. ‘We spoke to the usual suspects. A couple of lads said they’d heard of Marissa Lewis.’

‘How do you mean, “heard of”?’ asked Erika.

‘They said she’s had a reputation in the past for being the local bike – their words, not mine. One of them has a record, did three years for rape. The other has a record for assault, GBH. Both of them say they have an alibi, they were out until 6 a.m. this morning at a club in New Cross Gate, H20. They told us to check the club’s CCTV.’

Erika rolled her eyes.

‘Haitch 20. I know it. I’ve lost count of the times we’ve requested CCTV from them. Okay, get someone on it…’ She took another bite of the sandwich. ‘What the hell is in these sandwiches?’ she said, through a mouthful.

‘“Festive Christmas dinner sandwiches”, that’s all they had at the petrol station,’ said Rich.

Erika spat a mouthful out into the packet. ‘I can see the appeal in turkey and cranberry, even some stuffing, but who puts roast potato in a bloody sandwich?’

Erika dumped the rest of the packet in the bin. She looked around at the team, who had averted their eyes, not wanting to risk her wrath. Every other officer her age had taken leave to be with their family or other halves. She missed the continuity of the officers she regularly worked with. Detective Inspectors Moss and Peterson, and Sergeant Crane. She wondered fleetingly if they were having a good Christmas. She was pleased that McGorry was with her, but he was still a relative newbie – and even he had volunteered to stay, risking the wrath of his girlfriend waiting at home.

Her phone rang. It was a number she didn’t recognise, so she came out of the van. It was now dark, and the cold air caught at the back of her throat.

‘Hey Erika, this is Lee Graham.’

‘Hi, Merry Christmas,’ she said.

‘Merry Christmas to you too. I’ve drawn the short straw today, and I’m in the lab.’

Erika liked Lee. He was a forensics and computer expert in the Met police, and they had worked together on a few cases. There had been a frisson of flirtation between them, but nothing more. She wondered now if he was single, and if that was the reason he had decided to work on Christmas Day.

‘To what do I owe the pleasure?’ she asked.

‘Unfortunately, this isn’t a personal call. I saw your name on an urgent request for developing a camera film.’

‘Yes. How soon can you get it done?’

‘It’s already done. I’ve scanned them in, and I’m just emailing the photos over to your work email. I’ll get the hard copies over by snail mail.’

‘Thank you. I should buy you a drink sometime.’

‘Here’s hoping,’ he said.

Erika heard her phone beep. ‘I think I just got your email.’

‘Okay, I’ll let you go. Merry Christmas,’ he said and rang off.

She opened his email and scrolled through the attached photos. They were mostly taken from the tree opposite Marissa’s bedroom. There was a series of photos taken at night through Marissa’s bedroom window, where she was fresh out of the shower and wearing a towel, then naked and pulling on her underwear. There were also three photos, taken from above, of Marissa’s body lying in the snow. And three more at a lower angle, which looked like they were taken at ground level, close to, or inside, the front garden.

‘Joseph Pitkin, you lying little shit,’ said Erika. She walked over to the front gate of Marissa’s house, where the frozen blood in the front garden was rapidly being covered by fresh snow. She could see up into the tree, with its thick bare branches. ‘Was that your regular spot, to spy on her, Joseph?’ Erika looked at the photos again, and saw that Lee had included a message at the bottom of the email:

She was about to return to the van, when she caught an acrid smell of burning plastic. She looked around, and saw that at the end of the alleyway leading down to Joseph Pitkin’s house, smoke was rising into the sky.

Erika hurried down the alley towards it, the smell growing stronger. By the time she reached the back wall of the Pitkins’s house, thick black smoke was billowing into the air from behind the line of evergreens. She climbed up on to the wheelie bin, finding it much easier in the borrowed trainers, and pulled herself up onto the wall. Through the trees, she could see Joseph in his long coat, huddled over a burning oil drum. On the snowy ground beside him was a box of papers. He picked up a handful and dumped them into the drum, a shower of sparks and flames floating up into the dark sky. The windows in the house behind him were dark, and he was only lit by the glow of the flames.

Erika dropped down softly onto the strip of earth between the wall and the line of trees and stepped through. Joseph heard her feet crunch on the snow as she came towards him,

‘Stop what you’re doing. Right now,’ she said. He grabbed at a spade propped up against the oil drum, but she moved faster and grabbed it from him. She thought he would attempt to run, but he sank back onto the snow with his head between his hands as she put in a call to McGorry.