‘And keep pulling until Safa and Harry get through.’

‘Got it.’

‘And if the other doctor comes through by mistake, then just throw him back out.’

‘What?’ Doctor Watson says.

‘Eight minutes . . .’ Ben nods, sticks the mouthpiece in his mouth, nods again and runs for the window with big steps to avoid tripping over the half-size flippers on his feet. He dives forward with his arms outstretched and through once again into another world in another time and place.

‘Crazy bastard,’ Malcolm says once he’s gone.

Life is crazy and nuts and bizarre but fucking hell be like Harry and get on with it. Lock it down. Let it go. Be here in the now and dive through a time machine into a wild storm of an ocean and he would scream except his mouth is full.

He plummets and bellyflops into the valley of two waves and sinks beneath the surface with his stomach churning and his heart hammering. The buoyancy aid does its job. He surges back up, feeling an immense sense of relief. Then he remembers he is breathing from a tank so he doesn’t need to hold his breath.

Everything looks different now. He was just a bit higher a minute ago but that height made the world of difference. Now he’s at the bottom staring up in awe at the wave rolling towards him and he has to force himself to stay calm and get his bearings.

He twists and paddles for a second until he finds his square of light below and behind him, still in the trough of the waves. With the position of that light in mind, he starts swimming directly away from it, breathing fast and ragged through the mouthpiece.

The sessions in the tank pay off. The ability to withstand the current and not feel as if he is in a totally alien environment. He goes for what feels like a few minutes and glances back to see the square of light still seems to be in the same place so he swims harder and remembers to make use of the flippers properly.