The rubber seals of her mask sucked tight against her face. And locked.

She groped at the mask. Tried to take a breath. Nothing came, just more tightening of the seals and a familiar pressure under her sternum. She knew this feeling well from all her training sessions. No air was getting through. She fumbled at the side of the mask above her right ear. This wasn’t going to be a problem. The surface crew were pumping air down to her – she couldn’t run out. But just occasionally the umbilical got tangled with the positive/negative pressure lever on the mask and cut off the supply. It was easy to solve. If you kept calm. Easy.

Heart thudding she found the lever, flicked it down and went for another breath. Her ribs tried. Wouldn’t inflate. Quickly she snapped the lever back down.

Nothing.

Up. Nothing.

‘Sarge?’ Wellard sounded panicky. ‘What’s going on? What’s happening?’

But there was no air in her lungs to answer. Her arms were aching. Her head was pounding as if it had swollen to twice its size. Someone could have been standing on her chest. Her head jerked back, her mouth gaped. She groped for the switch block on the side of her vest. Tried to get her air supply to transfer to the Scuba bail-out system.

‘Sarge? I’ve opened all my valves but there’s air haemorrhaging from somewhere. Have you got pressure?’

She knew what would be happening up there. The standby diver would be fumbling himself into his equipment, getting his fingers tangled in the mask spiders in his panic, forgetting everything. Legs like jelly. He wouldn’t be in time for her. She had seconds left, not minutes.

Numbly she batted at the switchblock again. Couldn’t find it. Her head swelled harder and tighter now. Her limbs were tingling.