One of the windows in the bus shelter was boarded up with ply-board, which someone had unimaginatively sprayed their name on, replacing the dot on the ‘i’ with a marijuana leaf.

‘Some things never change,’ Kate commented, as Finn studied the bus-route map plastered on the portal next to the boarding.

He nodded at the graffiti. ‘Not a lover of urban art, then?’

She grunted. ‘How anyone can call that art is beyond me!’

‘Oh, I don’t know,’ he mused, ‘some of this stuff goes for a ton. Banksy and all that.’

‘It’s vandalism. And it’s ugly.’

‘It’s probably just kids acting out. It’s harmless.’

‘We’ll have to agree to disagree on that I’m afraid.’

‘Is this where…?’

Kate nodded, picturing the disturbing crime-scene photograph hanging in her living room. ‘Yeah, Willow Daniels was slumped up against this corner here. The pathologist reckoned she’d only been dead for six hours when she was discovered.’

‘Who found her?’

‘The bus driver on the first stop of the morning. He’d pulled in thinking she was waiting for the bus, but when she didn’t respond to him calling her, he got out and took a closer look. That’s when he realised she was naked and spotted the bruising around her throat, and called for help.’

‘Poor bastard.’

‘He was traumatised for weeks from all accounts. Treated for PTSD, or so the rumour went.’

‘And he was never a suspect?’

She shook her head. He had a cast-iron alibi, he’d been in central London watching a TV show being recorded. There were dozens of witnesses who corroborated he was there.’

Finn took a step back and surveyed the area. ‘It’s hard to imagine that someone was killed here. You’d never know looking at it. It looks like any number of grimy grey bus shelters across the country.’

‘Assuming he killed her here… this road isn’t busy during the night, but there would still have been cars travelling along it, so it’s unlikely this is where he committed the crime. It would only take one alert driver to see him throttling her. No, he’s smarter than that. Leaving her here was part of something bigger.’

‘What?’

Kate crouched down and looked at the seat the body had been propped on. ‘That’s just it, I have no idea. It always struck me as odd that he left her at this particular shelter.’

‘I don’t follow.’

She straightened up and turned to face the road. ‘Well, look at this place. Okay, it’s a public road, but there isn’t a property for a mile radius, right? So why did he choose to leave her here? If it was about displaying her in a public place, then there are far more public bus shelters up and down this road. But if it was about leaving her somewhere she wouldn’t be found, why pick a bus shelter in the first place? We spoke to the bus company who run this route, and they estimated that more than two hundred people use this particular stop each day, either to join or leave the bus. Of all the stops on this particular route, it isn’t the busiest stop, but it certainly isn’t the quietest. So why here? There has to be a reason he chose this particular stop.’

Finn puffed out his cheeks. ‘I don’t know how you lot do it. I’d just assume he picked it at random and move on.’

‘That’s where you’d be wrong, though. Nothing is ever just random. Even when we think we’re making a decision at random, our subconscious drives the decision. I’ll prove it to you. Pick a number between one and five.’

He frowned sceptically. ‘What will that prove?’

‘Trust me. I bet I can guess which number you’ll choose. In fact, your subconscious mind has already chosen. Go on.’

‘Got one.’

‘Four.’

‘Wait, how did you…?’

‘Simple. Whenever you give someone a range to choose from, they overthink it. They want to avoid the two named choices, so that rules out one and five in your so-called random selection. Now I’d say three is the obvious answer, but your sceptical outlook would want to prove me wrong, so you won’t go for the middle option, and suddenly your choice is between two or four. You strike me as someone who is generally quite optimistic about life, so I guessed you would choose the higher of the two options. There you have it: four.’

He narrowed his eyes. ‘What kind of witchcraft trickery is this?’

She nodded to the route map he’d been studying. ‘Plus this is the stop for the number 400 bus, so the number was already floating about in your head.’

He glared at her. ‘You tricked me.’

‘No, but I proved your random choice wasn’t random at all. Now, if we can just figure out why the hell he left her here, maybe we’ll move closer to figuring out who he is.’