Her heart beat low in her chest. She kept her breathing steady – too deep and she’d start to rise, too shallow and she’d lose buoyancy. Nothing should, or could, be moving down here: there were no currents in the quarry. Everything should be motionless. She began to swim towards where she’d seen the movement.

‘Sarge?’ Surfaceside, Wellard had noticed the diversion instantly. ‘Everything OK?’

‘Yeah, yeah. Give me another bar.’

As she went deeper it was Wellard’s job, as the panel operator, to increase the pressure of the air reaching her down the umbilical lead. She turned and shone the torch behind her, trying to see how far back the netting was. She was probably at about forty-seven metres deep and still going down. Just another three metres to the HSE limit. ‘Yeah – up it to sixteen.’

‘Sixteen bar? That’ll put you at-’

‘I know what it’ll put me at. Let me worry about it, not you.’

She swam on, her hands out now because she wasn’t sure what she was going to see. Forty-eight metres, forty-nine. She was at the place where the movement had been.

‘Sarge? Do you know what depth you’re at?’

‘Just hold it,’ she whispered. ‘Hold me steady.’

She turned the torch upwards and looked up. It was uncomfortable with her mask wanting to lift off and let water in. She pressed it to her face with her fingertips and stared into the effervescent silvery stream of bubbles marching determinedly above her in a long column – up towards a surface that was too far away to see. Something was in that column. She was sure of it. Something dark was swimming up through the procession of darkness and air. A shiver went through her. Were those the naked soles of someone’s feet?