I wonder why I didn’t see Dev at breakfast. What had security said when he reported that flicker of light along the security grid? It was probably nothing, like he thought.

Still, I clutch the black pearl at the base of my throat.

I remember the last words my mother ever said to me: We’ll be back before you know it. Then she and my father disappeared forever.

“Freshmen.” Dr. Hewett says the word like an insult.

He stands in the aisle, bracing himself with one hand on the seatback. He breathes heavily into the bus’s microphone. “This weekend’s trials will be very different from what you might be expecting.”

This gets our attention. Everybody fixes their eyes on Hewett.

The professor is shaped like a diving bell—narrow shoulders tapering down to a wide waist, where his rumpled dress shirt is half untucked from his slacks. His frazzled gray hair and sad, watery eyes make him look like Albert Einstein after a night of running failed calculations.

Next to me, Ester shuffles through her index cards. Top rests his head in her lap. His tail thumps softly against my thigh.

“In thirty minutes,” Hewett continues, “we will arrive in San Alejandro.”

He waits for our whispering to die down. We associate San Alejandro with shopping, movies, and Saturday-night karaoke, not end-of-year trials. But I suppose it makes sense we would start there. The school’s boat is usually moored in the harbor.

“We will proceed directly to the docks,” Hewett continues. “No detours, no side trips to buy refreshments. You will keep your phones off.”

A few kids grumble. Harding-Pencroft strictly controls all communication through the school intranet. The campus is a cellular dead zone. You want to look up the breeding habits of jellyfish? No problem. You want to watch YouTube? Good luck with that.

The teachers say this is to keep us focused on our work. I suspect it’s yet another security precaution, like the underwater grid, or the armed guards, or the drone surveillance. I don’t understand it, but it’s a fact of life.

Typically, when we get into town, we’re like dehydrated cattle at a watering hole. We stampede to the first place with free Wi-Fi and drink it in.

“I will have further instructions once we’re at sea,” Hewett says. “Suffice to say, today you’ll find out what the academy is truly about. And the academy will find out whether you can survive its requirements.”

I want to think Hewett is just trying to scare us. The problem is, he never makes idle threats. If he says we’ll have extra weekend homework, we do. If he predicts 90 percent of us will fail his next exam, we do.

Theoretical Marine Science should be a fun fluff class. We spend most of our time contemplating what ocean technology might look like in one or two hundred years. Or if science had taken a different course, what might have happened? What if Leonardo da Vinci had done more to develop sonar when he discovered it in 1490? What if the plans for Drebbel’s “diving boat” hadn’t been lost in the 1600s, or if Monturiol’s anaerobic steam-powered submarine hadn’t been scrapped for lack of funding in 1867? Would our technology today be more advanced?