“Suit up!” Professor Bruce shouts. “I want you all in that pool in two minutes.”

Leo and I don our equipment, which is cold and damp from the previous class. I’m wearing a thin, one-piece bathing suit, and I can feel my nipples poking through the material as I shiver.

Leo glances at my chest. I expect him to make a joke about it, but he looks away abruptly, tugging a little too hard on the strap of his face mask so the elastic snaps.

“Fuck,” he mutters.

“Problem?” Professor Bruce says at once.

“I broke the band on my face mask.”

“Figure it out,” the professor says coldly. “The point of this class is to adapt and overcome.”

“Swap with me,” I murmur to Leo. “Your head’s bigger than mine. I can just tie it in a knot.”

“I have a big head?” Leo laughs, trading masks with me.

“You’ve got the biggest head I’ve ever encountered, in all ways,” I tell him sweetly.

Leo chuckles and slips his mask into place. It’s full-face, and looks disturbingly like a gas mask, like we’re in the middle of a war or a plague. I knot the back of mine and force it down over my head. It’s too tight, but I can make it work.

Once we’ve got our flippers and tanks on, we drop down into the water.

Immediately, my heart begins to race. I haven’t even put my face under yet. Sensing my stress, Leo sticks right beside me. Even though he’s never done this before either, he already looks comfortable bobbing up and down in the water, as if his gear weighs nothing at all.

Professor Bruce gets into the pool with us. With his flippered feet and the powerful kicks of his legs keeping him buoyant, he looks like a burly frog.

He takes his respirator out so he can shout at us. “While we’re on the surface, we’ll practice hand signals, clearing our mask, and recovering our respirator. After that we’ll descend.”

He teaches us the signals for Ok, Stop, Level Off, Ascend, Descend, and Follow Me. Then he goes over the mask and regulator techniques.

It all seems to fly by much too quickly, and I wish he’d run through it again. With each new instruction, the one before seems to dissolve in my brain. It doesn’t help that I’m continually thinking of the hundred feet of empty water directly below.

“Do you understand it all?” Leo whispers to me.

“I . . . I think so.”

“Just copy me,” he says in his warm, reassuring tone. “I know what to do.”

A lot of people think that Leo is overconfident. But when he says he can do something, he’s almost always right. I’m keeping my heart rate under control because I trust him. I feel safe with him here beside me.

Too soon, it’s time to descend. I fit my regulator in place and follow Leo as Professor Bruce takes us down to the bottom of the pool in measured stages. He uses our newly-learned handsignals to tell us when to pause, when to pop our ears, and when to drop further down.

Every few feet we descend adds an immense amount of pressure from the weight of the water overhead. I try not to think how far it is to the surface. I try not to consider how dependent I am on the little tank of air strapped to my back.

Leo stays right beside me. The release of bubbles out of the side of his mask seems slow and steady. I try to match it, so I don’t hyperventilate and use my oxygen too quickly.

We sink the final distance to the bottom of the pool and sit cross-legged in a big circle, with Professor Bruce at the center. The dark-haired girl and her redheaded friend are still directly across from Leo and me. It’s hard to tell if they’re smiling or not beneath their masks. Hard to tell if they’re staring at us as much as it seems.

I try to feel the sense of calm weightlessness that’s supposed to be pleasurable in this activity. Shouldn’t diving be something like dancing?

It doesn’t feel like that to me. It feels like being encased in wet cement while breathing through a straw.

I’m relieved when Professor Bruce takes us back up to the surface.

That relief doesn’t last long—he lifts his mask to say, “This time we’re going to practice buddy breathing. If your regulator is broken or you’ve run out of air, you can make use of your partner’s. This is the signal that means, ‘I have no air.’ ” He demonstrates the slashing movement of the hand across the throat. “We’ll descend. Then I’ll come around and take half the tanks.”

My stomach lurches. I don’t in any way feel ready to be down there without any air.