Erika flashed her warrant card, and she and McGorry ducked under the police cordon. They started along the street, passing the rundown houses where neighbours watched from their doorsteps in various states of early morning dress, gawping at the police tape at the end of the road, and craning up the street to where uniformed officers milled around another police tape cordon.

Erika struggled to keep up with McGorry, finding the heels she’d put on for Christmas lunch had no grip on the icy pavement. She wished the weather was warm so she could take her shoes off and go barefoot.

‘It’s the worst day to close off the road; we’ve already had to turn people away who are coming to visit relatives…’ He glanced back and saw Erika gripping a nearby wall as she carefully picked her way along.

‘What?’ she said, when she’d caught up, noticing McGorry staring at her.

‘Nothing. You’re wearing heels,’ he said.

‘Great work, detective.’

‘No, you look great. I mean smart, really good…’

Erika scowled and went to move off, but slipped. McGorry grabbed her just as she was about to fall.

‘Do you want to take my arm?’ he asked. ‘The house is a little way down the end.’

‘Not really, but it might be quicker. And I don’t want to go arse over tit in front of uniform.’

She grabbed his arm and they moved off at a slower pace.

‘I wore heels, once,’ said McGorry.

‘You did?’

‘Six-inch stilettos. When I was at Hendon, we did a charity Christmas show. I played Lady Bracknell in The Importance of Being Earnest.’

Despite her annoyance, Erika smiled as she picked her way through the ice.

‘Six-inch stilettos? Isn’t Lady Bracknell meant to be a staid and stuffy elderly Victorian lady?’

‘I’m a size twelve. They were the only heels I could get for my feet,’ he said, indicating his large shoes.

‘How much did you raise for charity?’

‘Four hundred and seventy-three pounds fifty…’

‘Go on then, give me a bit of Lady Bracknell,’ said Erika.

‘A handbag?’ he said, affecting an upper-class old lady vibrato.

Erika shook her head and smiled, ‘I’m glad you didn’t give up your day job.’

She let go of his arm as they reached another police cordon ballooning out in front of a terraced house near the end of the street. A low wall and a tall snow-topped hedge obscured the front garden, and through the open gate they could see a crowd of forensics officers in their blue paper Tyvek suits. The officer at the cordon peered at Erika’s warrant card.

‘A DCI has already been called. He’s delayed, triple stabbing in Cat…’ she started.

‘Well, he’s not here, and I am,’ said Erika. The officer nodded and lifted the cordon. They went to the forensics van parked up on the pavement. Another uniformed officer, a stern middle-aged woman with a nose stud and cropped grey hair, handed them each a Tyvek suit. They took off their coats, draping them over the top of the van.

‘Bloody hell, it’s freezing, said McGorry, quickly stepping into the legs and pulling it up over his thin suit.

‘It got down to minus twelve last night,’ said the officer. Erika held on to the van, balanced on one foot, and pulled on the paper suit, but her left heel caught in the fabric and tore the leg as she pulled it up.

‘Shit!’

‘I’ll bag that up; here’s another one,’ said the officer, handing her a fresh suit. Erika took it and pulled it on, but the same thing happened again. ‘You should be in flats, especially on a day like this,’ the officer said.

Erika shot her a look, and McGorry looked away politely as she took a third suit, and successfully managed to get it on over her heels. She zipped it up, and they both pulled up the hoods. They put on shoe covers which, again, Erika found tricky, but once they were ready they moved to the front gate and entered the tiny, cramped front garden.

Isaac Strong, the forensic pathologist, was working in the small space with two assistants. He was a tall, thin man in his early forties. The widow’s peak of his dark brown hair poked out from under the hood of his Tyvek suit. He had long, thin eyebrows, which made him look constantly quizzical.

The blood-spattered body of a young woman was on her back under the bay window. Her long black coat lay open. The plummeting temperature during the night had frozen her spilled blood to the consistency of a ruby-red sorbet. Her throat had been sliced open, and this was where there was the most concentration of blood, stretching out in a pool underneath her. It saturated her thin green strapless dress, split up the left leg to reveal black stockings and suspenders, and it covered the bay window and sill above in a fine frosted spray.

‘Morning, Merry Christmas,’ said Isaac, shaking his head. His greeting hung awkwardly in the air. Erika looked back at the face of the young girl. Her face was frozen, figuratively and literally, in fear. Her lips were drawn back, and one of her front teeth was broken off close to the gum. Her eyes, though cloudy, were violet, and they were strikingly beautiful, even in death.

‘Do we know who she is?’ asked Erika.

‘Marissa Lewis, twenty-two years old,’ replied Isaac.

‘Is that a formal ID?’

‘Her mother discovered her body this morning, and there’s a driving licence in her wallet.’

Erika crouched down and took a closer look. A square vanity case with the initials ‘M.L.’ was half-buried in snow by the hedge, and beside it was a black high-heeled shoe. They were both marked up with plastic numbers.

‘Anyone touched the body?’

‘No,’ said McGorry. ‘I was first on the scene with uniform. The mother found her and said she didn’t touch anything.’

‘Do you have a time of death?’

‘The extreme cold is going to make it difficult,’ said Isaac. ‘Her throat was slashed with a very sharp blade, resulting in deep cuts and severing both carotid arteries on each side of the neck. You can see this led to rapid blood loss, and she would have bled out very quickly. On her right hand, the index finger is almost severed, and there are lacerations to the thumb, middle finger and arms, which indicates she put up her hands to defend herself.’

‘There’s no way out of the garden, apart from the gate, or through the front door,’ said McGorry. Erika saw that in addition to the window, the front door had a fine spray of frozen blood on its faded blue paintwork.

‘Are those her keys?’ she said, noticing a bunch of keys with a heart-shaped keyring.

‘Yes,’ said McGorry.

Erika closed her eyes for a moment, imagining what it must have been like, overpowered by a knife wielding maniac in this small enclosed space. She opened them again, and looked at Marissa’s face.

‘Her nose is broken,’ she said.

‘Yes. And her left cheek. We also found her front tooth, embedded in the gate post,’ said Isaac.

Erika and McGorry turned to look at the gate post, where a numbered marker was fixed halfway up. Clumps of snow clung to the brickwork. Next to it was a wheelie bin, and a recycling box stuffed with empty vodka bottles. Erika turned back to look at the house. The curtains were drawn, no lights were on.

‘Where’s the mother?’

‘At the neighbour’s house,’ said McGorry, indicating a terraced house diagonally across the street.

‘And we’re sure the victim lives here? She wasn’t visiting her mum for Christmas?’

‘We need to check that.’

‘We’re going to have difficulties moving her,’ said one of Isaac’s assistants, who had finished clearing the snow from the blood-spattered legs.

‘Why?’ asked Erika.

He looked up at her – a small man with large, intense brown eyes. He indicated the vast pool of frozen blood spreading out from under the body.

‘The blood. She’s frozen solid to the soil underneath.’