Locking his hands on either side of the handle, Nash centred his entire being on turning it. He drew upon every reserve of strength left in his body, and the flesh of his palms burned and tore as, shouting out to God, the universe, even Natalie, from somewhere the power came . . .

It gave!

Frantically, Nash spun the stubborn wheel.

He barely had time to whip his head back as the massive bulkhead door flew up in his face, its steel edge missing him by inches, as a belch of tightly compressed air blasted up through the hole, dragging a column of churning white water and Mia Carter in its wake.

In the near-darkness he only just managed to grab hold of her before she fell back through with the gout of expelled water. Mia was a dead weight and, clutching her limp body, he feared that he was too late, but then she jerked in his arms.

‘Hang in there!’ he yelled, turning her on her side to let her vomit.

She had just begun to suck in air when water began pouring down upon their heads. The top compartment was overflowing!

‘We gotta go!’

Hauling Mia upright, Nash leaned her against the wall, which was really the floor. Then he jumped up to grab the horizontal ladder, locked his legs under her arms and, with a roar, lifted her up.

‘Grab the ledge!’ he screamed. ‘Come on, Mia!’

With a sob, she flung out an arm, and then another, and hung there by her armpits. Dropping down, he seized her lower legs and pushed her up and over with a splash into the top compartment. Here she waited for him, half-drowned, and half-blinded by the light streaming in through the upper third of the access hole.

‘Almost there.’

Taking her under the shoulders, he pulled her through the hull and out to freedom.

Holding Mia in open water with the sky overhead and the rain at last abating, Nash could have been forgiven for thinking the worst was over. But escaping the dark clutches of the submarine was only a momentary respite.

‘Rob, I’m hypothermic,’ she slurred, barely audible over the din of the waterfall. ‘I’ve got to get warm.’

She was indeed desperately cold, with pale skin and a worrying bluish tinge to her lips. It would take at least a couple of hours for the sinkhole to fill to the brim, and there were no ropes, even had they the strength to climb them.

Swimming Mia around the hull, Nash dragged her up on the nose of the hangar door. It was here that he discovered the state of Mia’s wrists. Deep cuts and lacerations showed where she had rubbed away cable ties and flesh on the rusting metal.

He hugged her close to share his body heat, and tore strips off the sleeves of her shirt to bind the wounds on her wrists. Clinging together, they watched the waterfall tumble into the sinkhole.