She sighs, but knows she’s beat. Instead she busies herself helping us put on the underwater hazmat suits.

I look at the lake of foul sludge in distaste. “Are you sure we can actually swim in that?”

She chuckles. “It’s just on the surface, about four feet of it floating in a layer on top of the water. Once you clear that, you just have to swim.”

I suddenly see another obstacle I somehow never thought of. I’ve never been in water deeper or bigger than a bathtub. “I can’t swim.”

“Luckily, you don’t have to,” Lachlan says. “At least, not really. It only counts as swimming if you have to get to the surface to breathe. All you have to do here is not panic. You can do that, right?”

I remember the nanosand crushing me, filling my nose, my mouth, creeping toward my lungs. Will swimming be like that? Maybe not, but drowning will.

But “Right!” I say, of course. I hope I don’t let Lachlan down. I hope we both don’t let Ash down. “If . . . if I don’t make it, will you go on and still try to save him?” I ask Lachlan. I bite my lower lip, tense. If I’m gone—with my lens implants, my special undercover assignment—what motivation will he have for saving Ash?

I keep misjudging him. But what do I know of people anyway?

“I won’t let you not make it,” he says with a lighthearted wink. “But if you don’t, I’ll get your brother for you . . . or die trying.”

He makes it sound preposterously melodramatic, but I know he means it.

Lark helps us into the suits, and even before I plunge into the sludge I feel like I’m suffocating. The suit is made of some kind of biofilm that fuses seamlessly wherever the coded edges meet, sealing me inside what feels like a death chamber. When the mask goes on I almost panic. The second my desperate breathing starts to fog up the full-face mask, Lachlan catches one of my hands, Lark the other, like they’re in a race to be the first to soothe me. Their competition distracts me enough to make me stop worrying about the suit killing me. I stop hyperventilating and sigh in exasperation. That works, and I find I can breathe tolerably well even inside my latest prison.

“Ready?” Lachlan asks.

“No,” I say. “Not at all.”

He laughs, thinking I’m joking, and dives in head-first, certain I’ll follow him. That’s what happens when you get a reputation for bravery, I guess. Is that how courageous people persevere? They do one brave thing, and have to live up to their reputation ever after? It would be so much easier to be a coward. But harder to live with myself.

Alone, I turn to Lark. Something has been nagging me in the back of my mind. “You told me before you had something to tell me. What is it?” My voice is muffled beneath the mask.

Two lines crease, then quickly smooth between her golden eyebrows. “It’s . . . nothing. It can wait.” She flashes a brilliant smile and gives me a quick hug. “I’ll tell you later. Promise. Don’t worry. I’ll be looking after you, too.”

“What do you mean?”

She hesitates a moment, with a secret little smile. “Why, waiting here of course, to help you if you have to escape this way.” She touches my face, but it is remote through the hazmat mask.

Lachlan surfaces in the filth, beckoning me urgently.

Awkwardly, I plunge in after him.

Terrible blackness weighs me down, clings to me with its foulness so that even though I know none of it is touching my skin I feel deeply contaminated.

Then . . . wonderful lightness. I’m clean, pure, in a crystal weightless world. The wastewater pool is huge, but lights set along the walls beam inward, making a star pattern of silvery illumination. Is this swimming, this cool clear hovering that seems to strip all my cares away? I wish I could shrug out of the protective suit and feel the water on my skin.

Then I try to move, and I realize that this is an alien world. Only technology is keeping me alive down here. I have an abstract idea of how to swim, of course. I’ve seen vids of people swimming. I move my arms a certain way, I kick my legs. In my head, it makes sense.

My first arm stroke sends me spinning sideways. I try to kick, and somersault through the water. Lachlan grabs me and steadies me with one hand on the small of my back, one under my arm. I hold my breath and start to rise upward toward the ceiling of sludge. Lachlan pushes me down, and mimes a proper swimming technique. I try, but end up in a modified crawl, as if I’m scaling a weird kind of malleable wall. But it moves me along—however awkwardly—and we head toward a tunnel.

Once inside I can pull myself along the walls. It’s an animalistic kind of four-legged gallop, and would be fun if it wasn’t for our destination.

The rebreather built into the mask makes a gentle hum as I breathe. We’ve been underwater for a while now. What if the equipment fails? Even assuming I could swim, or manage to not suck water up my nose, there’s no route to fresh air.

Finally the tunnel opens up. And then up.

There’s a current here now, with water flowing from all the Center’s uses down to the main city system. Luckily the human waste goes through a separate pipe that just opens into the place we entered, so this is just runoff from sinks and such. During the day, Lark told us, the outward flow would be so strong that we couldn’t swim against it. At night, though, with a skeleton staff manning the Center, there’s little water use, and only a gentle flow for us to swim through.

That’s a good sign. Fewer people for us to contend with.

The tunnel narrows, branches, but as instructed we stick to the main one. It finally opens up in a bulb-shaped chamber with a multitude of pipes feeding into it. In the center of that is a hatch.

We’ve been under a long time. The air I’m breathing seems stale, and I’m starting to feel a strange hypnotic sensation, like my focus is expanding and contracting. Lights dance in front of my eyes. I see the water flowing in front of me . . . but it’s different water. That makes no sense. There is the slightly clouded water I’m swimming in (if this strange flailing crawl of mine can be considered swimming), and beyond that—no, on top of that—is another water, more clear, with a different, circular flow.

The edges of my vision dim and all I see is that other water. A light shines through it at an angle, making shadows of the things moving through it. Shapes, the size of my palm, shadows without color or solid form, moving in a unison so precise it must be mechanical. I squint at this vision, confused, trying to see it all more clearly. Is it here? Am I losing my mind?