They set up along one side of the tube, leaving the other to walk on. Maria took the first shift, each ninety minutes long. I put my sleeping bag down such that I was head-to-head with Adrienne's, and we held hands as we fell asleep.

"Leo, it's one in the morning, you're up," Anita told me as she shook me awake.

I opened my eyes, a little shocked to see a tiger shark above me in the darkness of the aquarium night. "I have it," I said as I sat up. She went to her sleeping bag on the other end while I fished around in my gear bag for...