Tusker stopped swimming and turned to face her in the dark water, being careful to stay below the surface. They’d gone over the tank handoff several times. She’d have the 100 percent O2 clipped on her right side. “Rich on the right,” he remembered from his old tech diving instructor in Michigan. He reached out and, with his fingers, found the double-ended dog clip on her harness and unclipped it, being careful not to lose his grip. One mistake here—a dropped tank, a mixup of the two deco bottles—and they’d have to abort, or worse, he would die breathing the wrong gas at the wrong depth. He transferred the oxygen cylinder to his own right side and clipped it to the D-rings on his shoulder strap and hip belt. Then he did the same with the 50 percent nitrox tank, moving it from Sam’s left to his own. The transfer of weight caused him to sink in the water and Sam to rise, but they’d accounted for this and she deflated her own wing while he moved the tanks. He momentarily gripped her on both forearms and squeezed a goodbye, hoping the gesture would convey all he wanted to say. She squeezed back. Then she was gone.

Tusker turned back to face the ship that loomed in front of him, invisible in the water. The other invisible ship, the HMAS Vampire, would be directly below him now, 350 feet down. Sebastian had pumped up the little 15-cubic-foot travel bottle as much as he could, but Tusker had breathed off of it for the ten-minute swim and needed it for the descent as well. He would discard it when he got to the wreck. There was no time to waste. He deflated his wing and sank like a stone, equalizing his ears every few feet. After three minutes, he quickly switched mouthpieces. He was now breathing off of his precious bottom gas mix. The clock was ticking.

Without an anchor line, and in complete darkness, he had no sense of where he would touch bottom. A few feet off and he’d descend right over the lip of the trench and keep going into 2,000 feet of water. He blindly fumbled for the backlight button on his dive computer and pressed it. The display showed 300 feet and dropping. He had to be getting close. Would he sense the Vampire as he did the Depth Charge?