Finn slammed on the brakes and gesticulated angrily out of the window. ‘You bloody idiot!’ He leaned back in. ‘Did you see that? He came out of nowhere.’

Kate hadn’t seen a thing. Her mind had been wandering again. She could feel Finn watching her, his eyes demanding a response. ‘Yeah, nowhere.’

‘The world’s gone mad,’ he continued. ‘It was bad enough when they were just on bikes, but skates?’

Her mind was whirring as she tried to blot out the spikes of nausea, but as the signs for Battersea loomed close, the feeling of dread grew.

‘Listen,’ Finn said eventually, ‘if you don’t mind, I’d rather stay in the car than come to her flat with you. It’s just…’ his voice faded as he struggled to explain.

She touched his hand. ‘It’s okay, Finn. I understand why you wouldn’t want to come back here. Just drop me as close as you can, and then you can be on your way. I’m sure your folks will be finished with Armitage by now. I really appreciate everything you’ve done today.’

He thanked her and pointed out of her window at a small alleyway between two shops. ‘If you dart up there, you can cut through to the flat in no time. With this traffic, it could be another twenty minutes before I can drive you there.’

Kate gathered her bag and thrust her crutch out of the door. She waited until Finn had pulled away from the kerb before tentatively heading towards the passageway. The closest tube station to Amy’s flat was Vauxhall, but it was a good ten minutes away on foot. They had extensively checked the security-camera footage at the station, but at no point had Amy passed that way that night. They had tracked her movements to the theatre, where she presumably met the killer, but despite reviewing every CCTV camera in and around that area, there was no trace of her after the theatre, until her body was discovered outside her flat later that night.

Amy hadn’t used the tube to get home, or if she had, she hadn’t used her Oyster card or contactless debit card to do so. But the theatre was nearly a two-mile walk from her home, and if that was how she’d travelled, they surely would have caught sight of her on camera footage, but there was no sign. They’d requested footage from each of the buses running that night, and had petitioned the London Taxi Company for details of which cabs were running in and around that time. It had been a massive operation, which Kate had unfortunately had little involvement in, but there was no way to confirm how Amy had made it home. Nor why she’d gone there instead of to her cover flat in Balham.

Two young black men wearing baseball caps suddenly appeared out of the passage, one chatting loudly on a phone, and the other wearing large headphones. The second eyed her before blowing a kiss as they continued on their way. Kate took a step closer to the passage, picturing Amy making her final journey through it.

It was no more than ten metres long, and opened out into a wider courtyard housing two cafés, a dry-cleaners and an Italian restaurant. Beyond the restaurant, a second passageway led Kate through to the back alley that ran behind two roads of local businesses. She made her way along the dark and grimy street, littered with empty drinks bottles, crisp packets and cigarette stubs.

As she closed her eyes, she could remember racing along this very stretch, flashes of blue light all around. She stopped where Amy’s body had been left; eyes open, hands by her sides, with a stab wound in her abdomen.

A cough over her shoulder caused her to spin in defensive anticipation. A young man in wire spectacles stood behind her. He was average height, and extremely thin, wearing a brown shirt beneath a yellow cardigan. He offered an awkward smile, on an acne-scarred face.

‘You’re blocking my way,’ he offered, pointing at the staircase up to the flats.

Kate instinctively shuffled to one side. ‘I’m sorry. Wait, you live here?’

He nodded, as he stepped towards the black metal staircase.

Kate reached for his arm. ‘I’m sorry, which flat is yours?’

He gave her a curious look. ‘Number seven… just up there.’

Before she could stop herself, Kate passed him a business card. ‘I’m DI Matthews. I’d like to come up.’

He rolled his eyes. ‘You’re here about that woman, aren’t you? I thought your lot were done with poking about.’ He sighed, before indicating for her to follow him up. ‘I really wish the landlord had warned me about the flat’s history before I signed the tenancy agreement. If I’d known the woman who lived here had been killed, I might have kept looking.’

Kate shrugged her shoulders apologetically, keen not to have to explain her real reason for wanting to poke around. If Armitage had any idea she was here, she’d suffer the consequences.

‘Are you going to be long?’ the young man enquired. ‘It’s just, I have other things to get on with today.’

‘I just need to look around and then I’ll be out of your hair,’ she promised, as he unlocked the door and held it open for her.

She squeezed through the doorway, and left him in the poky kitchen, as she proceeded through to the small living room, which led to the bathroom and bedroom. Although there were signs of attempted assault and Amy’s arms displayed defensive wounds, the murderer hadn’t managed penetrative sex before he’d killed her. But unlike the other women, Amy had put up more of a fight, and further bruising had been discovered on her back consistent with a fall.

Was it possible that Amy had invited the killer inside her flat? The SOCOs hadn’t found her blood inside, so had ruled it out, but had that been the wrong call? The place had been in such a state that it had been impossible to tell if there’d been a struggle.

Kate could feel her migraine returning; so many questions about that night remained unanswered, and she was unable to sort the truth from the supposition. Amy’s actions had been out of character, but so had the killer’s. Why had he left her in the alleyway when Vauxhall Park was only a stone’s throw away? What had stopped him taking her there?

The loud ringing of her phone interrupted Kate’s thoughts. ‘Hi, Trish.’

‘Hi, hun. Are you nearly finished? It’s gone three, and I’m shopped out. Are you still at the police station?’

‘Not exactly… Any chance you can pick me up outside Vauxhall tube station?’

‘Sure thing. Did you manage to accomplish what you wanted?’

Kate looked around the interior of the poky flat. ‘I’m afraid not. If anything I feel further from the truth than ever.’