Rust’s sneer was cut off as the object struck his head. I flicked all the switches and squinted against the sudden glare, staggering forward, tripping over everything in my path.

Blinking away afterimages and a sudden blurriness, I could make out Mia on the floor, supporting herself on one arm, the other hand clutching her crimson neck. Rust and his attacker were locked together on the floor, rolling, chairs tumbling around them. I fought off a moment’s disorientation. An unexpected sweetness filled my mouth, and either a distant alarm had gone off or my ears were ringing.

I pulled myself together and rushed in to grab Rust’s arms, trying to haul him off the other guy. Somehow, with a strength I hadn’t thought I owned, I managed it. As I pulled him clear of Demus, my older self swung his arm. He had hold of a hammer and the crunch it made against the side of Rust’s forehead was like nothing I’d ever heard or ever wanted to hear again. Rust went limp in my arms and fell bonelessly when I dropped him a moment later.

‘Mia?’ I turned toward her.

‘I’m OK.’ She took her hand from her neck, her fingers red. ‘I think . . .’

It looked to be a shallow cut. Blood wasn’t flooding down her neck or anything.

‘You’ll have a . . . lovely scar.’ Demus coughed. More blood ran from his mouth than came from Mia’s neck.

‘Are you . . . OK?’ I asked. He didn’t look OK.

‘Three people die here tonight.’ Demus lowered his gaze and mine followed it to the hilt of Rust’s machete, jutting from beneath Demus’s ribs. ‘Like I said.’

‘Shit. Look, don’t move. I’m calling an ambulance!’

He caught my wrist. ‘Don’t. It’s not you that calls them.’

I tried to pull free. ‘Enough with that! I changed things. Remember? This isn’t your time anymore. I’m not even you.’ I showed him my left wrist, sticky with blood from my self-inflicted cut.

‘Wait!’ Mia lurched to her feet. ‘All this was for nothing then . . . ?’

Demus ignored her. He reached forward with his other hand, wincing as the machete shifted. He pushed his left hand forward exposing the wrist and a faint white seam of scar. ‘You can always fool yourself, Nick. I showed you my right wrist before. You cut your left one. It’s the natural way to do it. Three people will die here. Just like I remember.’

‘But . . . you said I’d lose a friend.’

Demus nodded toward the body lying by the serving area. A pang of regret crossed his brow. ‘Jean Arnot. You said you were prepared to sacrifice someone “old” for someone young. Elton never forgives you for it. I’m sorry. You lose a friend. It’s silly. We were just kids, and I haven’t seen him for longer than you’ve been alive . . . but I still miss him.’

‘I don’t understand.’ Mia turned toward the body by the door as if only now noticing it. She looked lost.

I didn’t want to understand, but I started to. John’s father had been to see Elton’s dad to apologise for his wife’s behaviour. Mr Arnot did agency work as a security guard. John’s father had a laboratory that must sometimes need guards to fill gaps in the rota. Cruel chance had done the rest.

Mia started to walk toward the body, stopped and crossed to us.

‘Mia . . .’ Demus blinked away sudden tears. He lifted a hand to the hilt jutting from his side. His voice fell lower still. ‘I can’t speak to her. But you will, Nick. You’ll understand.’

‘You never did have a plan to go back,’ I said.

‘No.’ A whisper. The blood was spreading underneath him. I was watching myself die.

‘You need to be in hospital . . .’

A shake of the head. I had to lean in to hear him now. ‘The two of you have to erase today from your minds, Nick. It’s important. You can’t know these things. They’ll poison you both.’

‘But . . . I die here?’ Suddenly forty didn’t seem so old.

‘I knew this was the end for me, but I didn’t know how. I’m not brave enough to have done it knowing all the details, and to let it happen just as you saw it. Rub those memories out.’

‘Christ.’ Mia knelt beside me. ‘Nick? You came back to do this . . . for me?’ She looked at Demus as if truly seeing him as me for the first time. ‘You came here to die for me?’

He coughed and looked away. ‘Maybe my cancer returned. Maybe I found out after I came back that time travel may only work on living things, but they don’t live long afterward. It’s not a gentle process. The truth is that neither of you should know what I gave up or why. Neither of you want to know.’ He lay back, breath rasping through bloody lips, growing fainter with each cycle. It’s an odd thing to watch yourself die. It filled me with a dozen different feelings, none of which I have names for. His breathing grew so shallow that I thought he had gone, but Demus sucked in a deeper breath. ‘I’ve given you what you need. Take away the memories. Give yourself back your future. Live your lives.’

CHAPTER 23

We didn’t tell the others about Mr Arnot, or Demus, or Rust. Mia and I ran from the restaurant when Demus shuddered out his last breath. We found the others hurrying toward us down the corridor and we herded them back, leaving by the ground floor fire exit. Somehow, I had the presence of mind to retrieve the bag with Demus’s two headbands from the car park bushes, and then we walked, rather than ran, back toward the tube station and the taxi rank outside it.

None of us spoke much. Mia and I didn’t speak at all. My coat hid the bloodstains on my jumper. The great majority of the blood on Mia’s neck had come off the machete blade, and she wiped it away before anyone saw it. How much trouble we were in depended entirely on Elton. We were either free and clear, with the blame squarely at the feet of Rust and a mysterious man with no identity, or we were in over our heads with an endless and unanswerable mountain of questions and accusations to face.

Elton held his tongue. When they told him that his father was dead, and where he died, and when and how, he said nothing. He said nothing about it afterwards either. Not to me. Ever. He knew Demus would have known, but he never asked how much the man had told me. And although I could have told him that I hadn’t known his father was there, and I had done my best to save everyone, and that in the end I had given my life for it . . . the fact remained that Demus had known Jean Arnot would die there. And the fact remained that Demus gave his all to keep us as his own past, so that what he asked me to do would matter to the future of his Mia. And the chances were that a quarter of a century from now I would return to 1986, not knowing the details of that night in the laboratory, but being sure of two things. First, that I was prepared for three people who walked into that building not to walk out of it again. And second, that one of them would be me.

I met Mia in Richmond Park two days later. She called me to arrange it. It was further for her to come than for me, but she knew I wasn’t well and she said she could walk from her crazy aunt’s. It was cold and grey and threatening rain, but somehow neither of us wanted to be indoors. It felt too claustrophobic, what with the space that the guilt and unspoken accusations would take up.

She was waiting for me, the bench to either side of her still frosty. She’d come without makeup, and without hairspray her hair looked so different that for a moment I wasn’t sure who was sitting there.

‘How is he?’ I put the plastic bag with its heavy contents between us.

‘Angry,’ she said. ‘Sad. All the things you would expect.’

‘And you?’

‘The same.’ She pressed her lips into a bitter line. ‘You should have told me who Demus was from the very start. How much damage all of this would cause. I didn’t want any of it.’

‘I should have told you who he was as soon as I knew,’ I agreed. ‘The rest I didn’t know.’ I raised a hand in defence. ‘I know now. I will know when I come back . . . If I do. If me and Demus really are the same person, exactly. But that’s a loop I can’t get my head around right now.’ I patted the bag. ‘I’m going to take away the last couple of weeks. Rub out the memory of it all.’

‘Why?’ The stare she gave me was all suspicion. ‘That’s what he wanted you to do.’

I took out one of the headbands. ‘Mr Arnot is dead. I can’t bring him back. Nobody can. Demus gave his life to stop Rust taking yours. And Rust is dead. And that’s a good thing. I can’t feel sorry about that. So, if I don’t do what Demus asked me to . . . If I don’t do the last thing that I asked myself to do . . . then what would it all achieve?’ I drew a long breath. If things didn’t go how Demus remembered, then I wasn’t Demus. If I wasn’t Demus, then my chances of surviving leukaemia stopped being guaranteed and became statistically unlikely. If I said that to Mia, though, what kind of pressure would that lay on her? She had the power to save me, but asking her to do it was beyond me. ‘All I can see is that if I don’t blank these weeks just like he remembers doing, then it would mean that none of this was for anything. That you could still get hurt years from now and that I’d missed the chance to help someone I gave my life to save.’

‘I never asked—’