‘Goodbye, Dad.’

He crushed the sphere and as the stars coursed over his skin and along his arms, I gave a cry of anguish and collapsed against the door. I looked up and saw my boy being consumed by time.

‘Goodbye, little man,’ I cried. ‘Goodbye, son.’

And then he was gone.

I don’t know how long I stood there crying.

‘Sir?’ a voice said. ‘Excuse me, sir?’

I turned to see the nurse in the aperture. He looked at me sympathetically as I wiped my tears.

‘Your wife is coming round,’ he said.

I followed him, staggering back over the glass bridge. The city didn’t look so beautiful. It seemed complicated, alien, and frightening. My legs felt as though they might give out as we crossed the lobby and went into the medical bay where the forest simulation was still running.

The colour had returned to Beth’s face, but I could feel mine had been drained by grief. I took her hand and squeezed gently. Her eyes flickered and fluttered open.

My Beth. My beautiful Beth. As overjoyed as I was to have her back, I was grieving for my son and struggling with the sacrifice he’d made. I wouldn’t learn the full extent of it for many, many years, but it was already beyond comprehension. He had given everything to save his mother.

Beth focused on the strange world she’d woken to, and took in the trees and the sunlight falling between the leaves.

‘David?’ she said weakly. ‘Where am I?’

I had no idea. I couldn’t even tell her what year it was.

She looked at me and must have mistaken my tears of grief for ones of joy. I suppose some of them were.

‘It’s OK,’ she said. She squeezed my hand, and it was a boon to feel her strength returning. She soon realized something was wrong. ‘What’s the matter?’

How was I supposed to answer?

Chapter 58

Harri and Elliot stood in the cave, having heard Ben’s video recording. He told them the same story you’ve just read, but from his perspective. I’ve listened to the recording so many times, but it doesn’t give me enough. I want to know how he felt knowing he was leaving us behind, to understand how he felt about the sacrifice he’d made, but he explained it to them in very mechanistic, practical terms, perhaps to dissociate himself from the huge emotional implications of what he’d done.

Elliot was shaking with grief and anger, and Harri was shell-shocked.

‘So now you know,’ Ben said on screen. He put his fingers to his eyes and removed the amber contact lenses he’d worn for so many years, revealing Elliot’s electric-blue eyes.

‘Oh my god,’ Harri remarked.

‘You could have brought them back,’ Elliot responded coldly. ‘Bring them back. I want my mum and dad. Bring them back to me.’

‘And if I did, what would that do? Would you devote your life to unlocking the secret of time travel? I know you, Elliot. I am you. An older you, who has already walked the paths you’re yet to tread. I know you’ve already started working on a theory, a theory you’ve never shared with anyone. I know what you’re capable of.’