He turned a corner and kept walking, until he reached a door where the corridor ended. Looking in through a window, he spotted four hospital-style beds, all of them vacant, but noticed an airlock at the far end of the ward that clearly led into a separate isolation unit. He entered the room, squeezed inside the tiny airlock, before using a standard staff-access code to unlock the door beyond.

He found the other Mitchell lying there on a single-size cot, various pieces of medical equipment arranged around him and an intravenous tube taped to one wrist. Jeff half expected him to open his eyes and say Gotcha. It was exactly the same man he’d left waiting for him outside – but, at the same time, it wasn’t.

It was at that moment he decided to think of the man lying on the cot as ‘Present-Mitchell’. Working carefully, he pulled the tube loose from Present-Mitchell’s wrist. Present-Mitchell moaned and shifted in response.

‘Okay, Mitch, got to wake up.’ Present-Mitchell grunted and tried to push Jeff away with weak hands, as he tried to persuade him to sit up. The man’s eyes flickered open, but failed to focus on Jeff’s face. His paper pyjamas crinkled noisily as Jeff finally dragged him upright, and he nearly slid to the floor while being helped off the cot.

‘Hey . . .’ Present-Mitchell finally mumbled, looking around himself. ‘What . . . ?’

‘C’mon,’ Jeff urged. ‘Time to get moving.’ He propped Present-Mitchell up against one wall, then slapped him hard on the cheek, desperate to get him to focus. It wouldn’t be too long before those security teams he’d seen patrolling the grounds eventually worked their way round to the basement area.

Jeff pulled his hand back to deliver another slap, but Present-Mitchell reached out and grabbed hold of his wrist, spinning him around and locking one arm around his neck like a vice. Jeff was far too startled to resist.

‘What . . . ?’ Mitchell’s voice wavered, but his grip was remarkably strong, despite the drugs ‘. . . what the fuck are you doing with me?’

His grip suddenly loosened, and Jeff pulled free as Present-Mitchell crumpled to the floor, muttering something incomprehensible under his breath.

Jeff stepped around behind him, pulling him up under the shoulders. Present-Mitchell seemed to come awake once more, and feebly reached out in an attempt to steady himself. He didn’t resist this time, as Jeff helped him get upright, with one arm flung around Jeff’s shoulders.

‘Okay,’ Jeff gasped, turning them both around until they faced the airlock. ‘We’re getting out of here. You ready?’

Present-Mitchell shook his head like a man in a trance. ‘Jeff,’ he mumbled, ‘it’s you, isn’t it? What the fuck are you doing here?’

‘Getting you out of here. Weren’t you listening?’

‘Out?’ Mitchell coughed, then sneezed wetly. ‘Okay, good. But I need to lie down first . . .’

‘No!’ Jeff saw Present-Mitchell’s eyes start sliding shut again. As he dragg