‘Maybe.’ Mitchell shrugged. ‘At least I can’t think of any other explanation. The next thing I remembr is being revived, and I couldn’t believe it when I learned I’d been brought back into my own past. I remember staring through the window at things I was sure I’d never see again – things like trees, birds, grass. They started interrogating me straight away, but there wasn’t much I could tell them.’

‘Then you broke out?’

‘I had to, because by then I’d started to remember things. After that, it was just a matter of time before I figured a way out.’

‘And then you came looking for me,’ said Jeff.

Mitchell smiled softly. ‘And then I came looking for you.’

Jeff had hugged himself, as if warding off a chill.

A metal panel, set into Arcorex’s main entrance, flashed from red to green as Jeff approached. He half expected alarms to begin blaring the moment he crossed the threshold, but, once again, nothing happened.

Get a grip, he told himself. As far as anyone else was concerned, he was just another member of staff coming in for an all-nighter.

Jeff swiftly crossed an atrium, partly lit by moonlight spilling down through angled panes of glass, and walked past a reception area, where a single security guard sat on a mesh-backed chair. The man flicked his eyes towards the new arrival for a moment, then returned his attention to a bank of screens. Jeff gave him a bare nod and continued across the expanse of polished marble until he arrived at a row of elevators.

As the elevator carried him below ground level, his UP began flashing a standard warning that he was now entering a high-security area. When the doors hissed open, he found himself at one end of a whitewashed corridor that was bleakly illuminated by strip lights. Mitchell had said he remembered seeing the letters B3 painted on one wall, which would mean he had been held in the lowest basement level, where all artefacts from Site 17, and other far-future locations, were analysed under strictly controlled conditions.

He moved further down the corridor, peering in through windows at labs where often incomprehensible alien machinery was X-rayed, chemically tested, blasted with radiation or simply picked apart by teams of engineers. He finally stopped and looked around, feeling frustrated. There was nowhere they could possibly be keeping Mitchell down here. In that case, how could he . . . ?

Of course. How could he have forgotten? Beyond the labs, there was an emergency ward at the very far end of the corridor; but, given Arcorex’s excellent safety record, the ward had never been used – at least until now. If they were going to keep Mitchell anywhere, it would be there.