Kate elevated her foot at the end of the bed and rested her head against a pillow, but despite her best efforts to clear her mind, her brain continued to fire. Closing her eyelids, she inhaled deeply through her nose, exhaling slowly though her mouth. She rolled onto her side to try and stem the throb of her ankle, but it didn’t help. Amy’s lifeless face filled her mind; it haunted her every thought.

Forcing herself up as frustration took its toll, she headed to the kitchen, picking up the bottle of painkillers. It had only been an hour since she’d last taken one of the pills, but it had done nothing to ease the ache in her ankle, head or heart. Opening the bottle, she dropped another pill onto her tongue, washing it down with a mouthful of tap water.

Not hungry, but wanting to be occupied, Kate searched the fridge for anything she could snack on. Nothing appealed. Reaching for the open bottle of wine, she tucked it under her arm as she slowly made her way to the living room. If her mind wouldn’t still, maybe she could distract it with television. Dropping to the sofa, she stretched her body out on the cushions, and poured a glass of wine.

After five minutes of channel-hopping, she turned the television off, throwing the remote at the armchair. Enough was enough. She wouldn’t be able to rest until she’d looked back through the evidence she couldn’t forget.

Sliding the two boxes along the carpet from the spare room to the living room, she welcomed the musty smell as she lifted the lid of the first box. Before the move from London, she’d very carefully boxed up the paperwork in chronological order, knowing one day she’d feel compelled to re-examine it. Her hand hovered over the first file. Was she really ready to pick this scab? Not only was it the investigation which had ended her stint in the Met, it was the unsolved case she’d spent a year trying to block out of her memory.

Taking a large gulp of wine, she lifted the first folder out and opened it. The bright, smiling face of Willow Daniels stared back up at her. Kate delicately ran a finger over the contours of the face, remembering how much Willow had resembled Mrs Daniels.

She shuddered as she slid the photograph aside, staring down at the autopsy image, the yellow-purple bruising clearly evident around her neck and collarbone. Murdered only weeks after her twenty-first birthday, she’d had her whole life ahead of her before the Metropolitan Killer struck.

Kate read her summary notes. In late August 2015, Willow had been partying with friends in Watford town centre, visiting half a dozen pubs before ending up in the town’s biggest nightclub. They’d been out celebrating one of the group’s birthdays. Just the girls, no boyfriends allowed. Her body was discovered less than half a mile from her home, naked and dumped on a seat in a bus shelter. Kate removed the next photograph, a mugshot of a lad in his early twenties: Willow’s ex-boyfriend. The original investigative team pegged him as their prime suspect, and arrested him within a week of the discovery of Willow’s body. A bricklayer by trade, he was already known to the local uniform patrol for anti-social behaviour offences. Under interview he’d admitted to being in the town centre on the night in question, but claimed not to have seen Willow in the week leading up to the attack. The team had noted that he’d come across as cocksure and arrogant in their initial meeting.

When CCTV near the nightclub was reviewed, Willow could be seen in a heated argument with her ex on the night of the attack. Under caution, the bricklayer admitted to seeing her at the club, but claimed their argument was born out of drunken jealousy on his part. He still loved her and wanted them to get back together, but she wasn’t prepared to discuss their future there and then.

Kate lowered her notes. Rhys Leonard had said something similar about him and Helen today, hadn’t he?

Parking the thought, she continued reading. Willow’s ex claimed he’d gone straight home, a mile and a half’s walk from the club, yet his car was later seen on a traffic camera close to Willow’s parents’ house, where she was living at the time. He was dragged back in and this time admitted that he’d got home, but had driven back to the club to try and find Willow, only to discover that she’d already headed home. Parking at her parents’ house to await her return, he’d fallen asleep behind the wheel, and didn’t wake until dawn, at which point he’d driven back to his flat.

Kate grabbed a packet of Blu-Tack and stuck the three images to her main wall, along with a printed map of Watford from the file. The club was in the heart of the town, and while Willow’s parents’ house was north of that, the suspect’s house was to the west.

Willow’s friends confirmed she’d left the club at 1.00 a.m. to make the mile-long journey home on foot, and should have cut through a children’s playground on her way. She’d been a confident young woman who knew the streets around her home, and wasn’t worried about being set upon. But she’d never made it. Although her body was found shortly before 6.00 a.m., the pathologist concluded she’d been killed between 1.00 a.m. and 2.00 a.m. Plenty of time for her ex to have carried out the deed.

Kate reached for her glass of wine as she studied the images on the wall. Her team had interviewed the ex-boyfriend after she’d taken over the investigation. Despite him having the motive and opportunity to commit the murder, there was insufficient evidence to bring charges. The nature of the bruising around the neck meant they were looking for a killer with larger than average hands and long fingers, and his were neither. Kate tacked each page of the pathologist’s report to the wall, carefully reading each word, as they began to swirl on the page before her.

She lowered her glass and slumped back to the floor, removing the second file. Roxie O’Brien’s profile stared back at her. Kate lifted the image and compared it to the one of Willow hanging from the wall. It was easy to see why the murders weren’t originally connected. Facially, O’Brien and Willow bore little resemblance; Willow was petite and brunette, while O’Brien was slightly overweight with deep auburn hair. Then there was the gap of twenty-four years in their ages, the fact that they had no mutual friends and lived in different parts of the city. There was nothing obvious to connect them. O’Brien was a hairdresser and nail technician, running a salon with her best friend and housemate, while Willow worked in a local gym.

O’Brien’s body was found in September 2015, beneath a tree in Hilly Fields Park, a wide expanse of green in Lewisham, with a view of Canary Wharf on the horizon. What made the discovery of the body more sinister was the presence of an all-girls secondary school on the south-east corner of the park. Many of the students walked across the grass as part of their daily route to school.

As with Willow, O’Brien’s body was discovered within walking distance of her home, as if the killer had been following her when he’d struck. But what had motivated the attack? Had he chosen her at random, or was there something in particular that he’d been searching for? A claw hammer was used to cave in O’Brien’s skull, though the lack of spatter on the area surrounding the body confirmed she’d been killed elsewhere.

In fact, the only similarity between the attacks was the fact that both victims were left naked, and in a public area. But it was enough for Kate to link them when a third victim was discovered a month later in Finsbury Park.

Kate’s vision blurred as the memories of that chilly and damp October morning flooded her mind. The naked body left on its side, squashed up against a wire fence, robbing the victim of all dignity. She held the scene-of-crime photograph in her hands, running a finger along the slash in the victim’s throat. Cut from ear to ear, she would have quickly bled out, choking on the blood as it filled her throat. Gasping for life would only have sped up the process. Did he watch as the life drained out of her body? Was that his thrill? Her final image would have been of his face.

Reaching for her glass again, Kate stretched her leg out, but unable to make herself comfortable, she sat on the floor; her blasted ankle still throbbed with pain. Dragging herself onto the armchair, she reached for the bottle of pills. He might as well have prescribed placebos for the effect they were having. She drained her glass before refilling it, and reached for her case notes.

Steph Graham was twenty-five, obese and lived in a flat above a takeaway on the Seven Sisters Road, a ten-minute walk from where her body was discovered. Born in the UK to Nigerian parents, Steph looked even less like Willow than O’Brien did. Graham’s murder was the first major investigation DC Amy Spencer had been part of, and Kate had welcomed her youthful exuberance and eagerness to learn.

Kate let out an inaudible sigh as the memories of Amy’s own murder on that cold January night tormented her mind. The anguish she felt was as strong now as the moment she’d received the phone call. How could she be dead? How could he have found her without them realising? How could she have let this happen?

Steph was Amy’s first murder case and Kate should have picked up on the young detective’s downward spiral behind her determination, but she’d been too caught up in her own private battles, maintaining control of the investigation against the invisible forces yearning for her to fail. If only she’d been more attentive. If only she’d heard Amy’s messages that night.

If only…

The sound of rain pattering against the living room window caught Kate’s attention and brought her back to the room. The night sky looked even darker, and although she’d switched on the electric radiator, the room felt icy.

Picking up the remote, she scrolled though her shows and started the Crimewatch recording again. This time she fast-forwarded the introduction and paused the screen when it reached the reconstructed crime scene outside Amy’s flat. She compared her copy of the crime-scene photo to the image on-screen, but she still couldn’t see what had alerted her subconscious mind on Thursday night. She was certain there was something she was missing, but as hard as she tried to focus, her brain just swam with wine, painkillers and guilt.