For a few minutes, it actually feels nice to Ben, using muscles and doing something.

‘Stretches,’ she says, moving them away from the bunker towards the open space at the end. They start with arm circles. Small rotations that grow larger but too slowly and within seconds Ben’s shoulders are burning from the exertion. They stop and reverse the cycle, which gives a second or two of respite before the pain kicks in. They bend over, stretching hamstrings, lifting feet to clutch and stretch the front thigh muscles. Arms spinning again then stretching overhead side to side and by that time the sweat is running freely down Ben’s red face.

‘Line up.’ She motions to the imaginary start line at the end of the bunker. ‘Jogging again.’

They set off just a smidgen faster than the last time, reach the end and jog back down. ‘Faster.’

They go to the end and back down.

‘Faster.’

Up and down.

‘Faster.’

The jogging becomes running then just short of a full-on sprint but she keeps them going until Ben’s legs are hurting and his chest is clamouring for air.

‘Rest.’

She stops for a minute, hardly showing signs of exertion apart from her face holding a layer of glistening sweat. An assessment undertaken. Harry’s fitness is very good. He is breathing hard but then he’s a big man. Ben has no fitness. None at all. How far will he push himself?

‘Ready? Again.’

They jog up and jog down. They run up and run down. Ben can’t keep up with them. His chest hurts. His legs feel like jelly.

‘Back up,’ she says, reaching the start line and twisting on the spot. Ben turns and runs, pumping his arms while gasping for air. Harry breathing hard and his face flushing from the heat but he keeps pace with her to the end.

‘Back down.’

They turn and run. Ben’s head starts to swim. He staggers with a wave of dizziness going through his head until gravity takes over and brings him down to the soft grass, where he lies panting and feeling like he is going to die.

‘That’s enough,’ she says from somewhere nearby. ‘Take a couple of minutes. I’ll get water.’ She heads inside, leaving him flat out on the grass and Harry leaning with his back against the bunker, panting through an open mouth. They don’t speak. Ben is in too much pain. She comes out carrying three big cups of water. Ben gulps his down, feeling the coolness of the water cascade down his parched throat.

‘Over here,’ she says as soon as his cup is drained. He rises up and staggers towards her.

‘Circuits, ten push-ups, ten sit-ups, rest, repeat, ten push-ups, ten sit-ups, rest, repeat . . . got it?’

‘Only ten?’ Harry asks, dropping down into position.

‘For now,’ she says, nodding for Ben to copy her. ‘Three, two, one . . . go!’