They both stop dead, just a few feet in front of me. Kit is a step closer, close enough for me to witness the shock flooding his pale features. He’s let himself go in his eight days of lying low, excursions limited to late-night walks in the dark with Melia along the deserted river path. He’s needed the human contact, needed his Melia maintenance. I haven’t asked her if she’s slept with him, but it seems unlikely that she would have undressed in some squalid hostel. A kiss, perhaps, with this bearded, semi-vagrant Kit.

It’s good he looks so rough. That will help.

He has recognized me, of course, and is instantly combative, an animal sensing a trap. ‘What the fuck are you doing down here, you prick?’ His voice has the hoarseness of disuse. He turns to Melia, anger and panic exploding from him: ‘Can you believe this? This is a fucking disaster, Me!’

‘Kit, wait—’ she begins, but he speaks over her, spinning back to me, his mouth twisted with contempt.

‘Why are you lying in wait like some fucking psycho? What do you want?’

‘I’m not lying in wait, don’t flatter yourself.’ My tone is lethally cold. ‘I’ve just been to the New Year’s party at the Hope and Anchor. Getting some air before I head home. Back to my lovely Georgian townhouse.’

Though the line about the party is rehearsed, the taunting detail about the house is unexpectedly real, a last opportunity to lord it over him. I watch him grapple with the claim that this meeting is coincidental. He wants to believe it. He has little choice but to believe it.

‘Kit.’ Melia tries again, but he ignores her and edges closer to me, so close I can smell the confinement on him, humid and sour.

‘Don’t you tell a soul you’ve seen me, all right? I need your word on that, Jamie.’

‘Or else?’

‘Or else I’ll kill you.’ His eyes flick to the river. He would do it, as well. He would tip me over the wall and watch me drown. I picture my own face on the surface, stealing a final breath before the water turns it black, and suddenly, before anything, above all else, I crave a confession.

‘I know what you’re doing,’ I say, straying from the script. ‘You’re in hiding, you can only come out at night like the vampire you are. You’re setting me up.’ My voice breaks with sudden, rogue emotion: the lowest, bleakest sense of lost friendship, of betrayal. I’m breathing heavily, starting to forget Melia is there. ‘You really would see me rot in jail, wouldn’t you? Just for a payout.’

‘What the fuck?’ He denies it, of course. ‘You’re losing your mind, Jamie. Must be dementia at your age, eh? Just go home, yeah. Forget this happened. No one would believe you, anyway – I hear the police are all over you already.’

I brace, feel the strength gathering in my shoulders. ‘I’m not going anywhere. Not until I hear it from your lips, that you’ve set me up.’

He continues to protest, at the same time shoving me, so I slam against the river wall, adrenaline stifling the worst of the pain. Our body heat is magnetic, we’re clinging as if we’re down a well together, nothing to clutch but each other. This is not brawling, as it was on the boat, but mutual primitive terror. ‘Say it,’ I growl. ‘Say it.’

A figure moves in my peripheral vision with a dancer’s grace, a steel blade raised that will slice through clothing like butter. The angle of entry has been studied on websites that supply such information, googled on borrowed devices.

There is an instant of acute horror when Melia looks beyond him to me and I think, She’s going for me, not him, but it’s delirium, of course, the final, most fantastical projection of my paranoia.

She loves me.

She chose me.

Now Kit utters a succession of noises unconnected to rational language. I couldn’t have asked for a more perfect expression on his face as he collapses against me: surprise dawning, but not allowed fully to rise. A beautiful sunrise blotted by a flock of swallows – or maybe a toxic ash cloud.

I step back and let go of him, and he’s falling to the ground with a heavy thwack. He’s remembering language and saying my name, begging for help, crying for his mum. But all too soon his airways are filling with blood and he can no longer voice his terror. There’s a scraping noise from one of his hands, before defter fingers than his remove something from his grip – a phone. Then, with a clean arc, it flies over the wall into the water.

An arrow of steel follows.

We wait, and, as his final breaths are drawn at our feet, we stare down at him. Bless him, I think, unexpectedly. There was no guarantee I’d be found guilty – or even charged – and without a body there’d have been those seven years to endure before he could be declared dead and the insurance payment made. That’s trust for you. That’s love. Of course, his clear preference was for plan A, the swifter, more ruthless solution. All he’d have needed then was his new passport and he’d have been off somewhere hot and cheap while he waited for Melia to join him.

Sorry, Kit, there’s no passport. A murder conviction without any evidence of human remains? Come on, that happens once in a blue moon. Of course insurance companies want a body.

And that’s what they’re going to get.

‘Let’s get this finished,’ Melia says, and together we drag him behind the shrubbery on the far side of the path. There is blood by the wall, but that can’t be removed and in any case may prove a useful guide for the early-morning runners and dogwalkers who will stride past in a matter of hours, hungover and resolved to cleaning up their act. New Year, New Me. One of them will find him, led by a dog’s inquisitive nose, if not their own eyes.

When the police tell Melia where Kit’s body has been found, she will confess she knows the spot. She knows it because he has told her he meets his dealer here. She doesn’t know the dealer’s name, no, but she’ll remind them of his debts – debts that any financial investigator can confirm. She’s feared that since his disappearance he’s fallen into semi-vagrancy, like some of the other addicts she’s seen; she’s searched and searched – even going out in the dead of night – but never been able to find him. She’s been so worried, what with knife crime being on the rise, practically an epidemic.

‘Are you all right?’ I ask her.

‘Yes, I think so. You?’

‘Can’t stop shaking.’

I feel her grip on my arm, firm and steadying. ‘Keep going.’

In the breath of the sleeping river, we change out of our clothes and shoes and into fresh ones carried by Melia in her pack. The old go in the pack and are tossed into the water. At home, I’ll undress and put everything in the washing machine, just in case some fibre from him, some spot of blood, has attached itself. Melia will do the same.

We’ve been through the scenario, the psychology, scores of times, we both know the script by heart, but I still confirm my next line before we part. ‘As soon as I hear he’s been found, I’ll send you a text message of condolence. Clare and I will send you a card.’

‘Thank you.’ There’s grace in those two words, a sense of something still spared for her former lover. ‘I’ll invite you to the funeral. You and Clare.’

‘We’ll come.’