He examined the niche first, going so far as to press himself into it to see if it activated any kind of device. The chiseled stone around him remained innocuous. He sank lower still. The silt he’d kicked up earlier had settled back to the bottom. He cleared away an area where the wall met the floor. And something caught his attention. He pulled his dive knife from the sheath strapped to his calf and ran it along the seam. The tip vanished into a tiny gap between the floor and wall. He tried again at another spot and found the same thing.

Three more attempts convinced him that the floor of the Treasure Pit was fitted like a plug. There was something deeper in the earth, something buried below this false bottom.

He thought for a moment. There had to be a way to get there. The Ronishes had figured it out. Cabrillo swam a slow circuit of the floor, his dive light shining on the joint. It was in a corner. A stone was wedged tightly between the floor and a small irregularity projecting from the wall.

Juan didn’t touch it. Instead, he pulled his knees up to his chest and thrust them down onto the floor. The impact sent pain shooting up from his heels but also made the entire floor of the pit bobble ever so slightly. He glanced back up at the niche.

Clever, he thought. Very, very clever.

He returned to the rock wedge and got himself ready. He had no idea how much time he had, but he assumed he’d have to be quick. Reaching out a hand, he pulled the stone free, then finned for the grotto as fast as he could. Where a second ago all he could hear was the sound of his breathing, the pit was suddenly filled with the scrape of stone against stone.

The bottom of the chamber was an enormous float, kept in place by the wedge. Juan threw himself into the niche just as the silt-covered floor reached it. He pressed himself as far back as possible. The pit’s designers hadn’t had bulky scuba tanks, so the fit was tight. He watched in awe as the floor rose higher and higher. It climbed past his knees, then waist, and continued upward. It wasn’t so buoyant that it raced for the surface, but rather it ascended at a stately pace.

He realized that his fiber-optic cable was trapped between the float and the wall, and said a silent prayer that it wouldn’t get cut. No sooner had he thought it than the frayed end drifted down over him, the plastic abraded away. A second later, the loose end of his lifeline drifted past, too.

He had no idea how the float would stop but he figured it must, otherwise the Ronish brothers would have perished down here seventy years ago.