The energy of my step drives the swing of the hammer, and the window explodes.

I lean out into the night and suck in the air. It’s cold as deep water, and it fills my lungs like life. I use the hammerhead to clear as much of the glass from the frame as I can, but as soon as I try to pull Marcus closer, it’s clear that I can’t do it with one hand. I should be distraught, emotionally overwhelmed, but all my remaining mental strength has been honed to a fine point, to completing a single set of things I need to do, and I feel nothing. I take another breath of the air outside, then go back into the hall and down one flight.

After the impenetrable darkness of the cellars, the dusk up here barely slows me down. I go to Gretchen’s room next, still feeling unsteady, but I crash into the door like a battering ram, turning my shoulder into it at the last second. The latch holds, but the door itself cracks along a seam where I hit it. I use the hammer to clear the wood, then reach in and unlatch the door.

Gretchen is huddled on the bed under a protective mound of blankets. I practically throw the hammer through her window, take another breath past the shattered remains, and turn around, only then seeing that there is another figure curled up on the floor beside the bed. I bend, trying to get my eyes to focus.

It’s Kristen.

Dimly, I think another piece of the puzzle has slotted into place.

But I can’t abandon Brad, even if Kristen wants nothing more to do with him. I go back out, moving down the hall to the last door. I’m flagging now. I can feel it, and it’s not just tiredness. My movement is sloppy, my balance precarious, and my mind is wandering. It’s the gas. It’s in my lungs, my blood. I hit the door to Brad’s room, but I’ve lost all the punch I had a moment ago, and it holds. I try again to no avail. I’m suddenly impossibly tired. It’s like being carried away on a thick black river and wanting nothing more than to float with the current. I try once more, but my shoulder charge is weak and uneven. I hit my face against the jamb and collapse to my knees.

I have no choice. I need air. I crawl back the way I came, back into Gretchen’s room, clambering roughly over Kristen’s prone body to lay my head on the windowsill and drink in the night. A shard of the windowpane gouges my cheek, but I stay where I am, breathing deep and full until my head clears, and I remember the O2 tank I left in the hall upstairs. I stagger out, flounder my way up the steps, and pick it up. I fiddle with the regulator, taking a quick hit as I make my way back to Marcus, and the oxygen hits my brain like an adrenaline firework.

I roll Marcus onto his back and clamp the regulator to his face.

“Breathe,” I say. “Breathe.”

And then I’m moving back into the hall and down once more, wondering vaguely if that delay will cost Brad his life or if he’s dead already. I am lining up to charge the door when a firm hand grips my shoulder and spins me round.

Chapter Thirty-Four

I don’t know what woke me. It wasn’t a sound as such, or not one I consciously recognized when I opened my eyes. For a while I lay in bed, straining my ears to focus, and then there was something: a muffled thud, like someone overturning a soft but heavy chair. It came from below.

I had my little stub of candle in its holder and had borrowed a box of safety matches from the kitchen, the waxed kind that smelled of paraffin. I struck one and lit the candle, then swung my legs out of bed and planted them firmly on the floor. I don’t recall really deciding to do anything, and I think I might have still been half-asleep, just acting without really thinking.

I could have wrapped a towel around myself and stuck my head out into the hall, but I didn’t like the feeling of being naked, or nearly naked, after what had happened to Gretchen. So before I opened the door, I dressed: bra, underwear, a sundress, and sandals. It took me barely longer than the towel would, and I felt somehow secure, like a person ready to face the world. Still, it was a strange decision, and I don’t think I was thinking clearly. My head felt thick, fogged by more than sleep, and my feet were unsteady, as if I was drunk.

I stepped out into the hall and along to the spiral staircase, my candle flame fluttering so the shadows leaped. I thought vaguely of what Marcus had said about Plato’s cave, about taking the shadows for the thing itself, but my brain was too sleepy to do anything with the image. Instead I tiptoed down into the foyer and looked around. The front door looked solidly locked, but it felt strange to be down there alone in the dark, and I couldn’t remember why I had come down.

A sound, I thought. I had heard a sound.

Suddenly I wanted to get this over as soon as possible. I might have gone back up the stairs if the candlelight hadn’t caught the odd flash of green on the ground.

A garden hose, like one I’d seen in the basement. It seemed to be running from the cellar stairs into the living room.

I wasn’t scared, just curious, as if I were still in a dream where things didn’t really make sense but everyone behaved as if they did.

I followed the hose into the living room.

I could tell something was off as soon as I went in. Moonlight came through the great high windows, and I could see something out of place in the middle of the living room carpet—a sprawling, mounded something, like a large dog stretched out and fast asleep. If my eyes had been better I wouldn’t have needed to stoop to see what it was, wouldn’t have had to touch him, to roll him over, feeling the warm wetness on my hands and smelling the sharp, metallic tang of the blood all over him.

“Brad!” I gasped, kneeling beside him.

If I’d had my glasses, I wouldn’t have had to kneel, and I might have noticed the figure I had walked past to get to him, might have sensed them moving behind me before the blow fell. The back of my head flared with sudden agony, and the world went first light, and then very, very dark.

Chapter Thirty-Five

The hand on my shoulder belongs to Melissa. She’s holding a battery-powered lantern and is standing at the top of the stairs, looking perplexed and angry.

“What the hell is going on?” she says. “Did you break something?”

“The windows,” I said. “We have to get this door open.”

“What are you talking about?”

“Just help me with this door.”

“It’s locked.”

“Force it!”

She knocks, and I push her aside and charge the door again. This time it shudders in its frame.

“Jan! What the hell!” Melissa exclaims.

I hit the door twice more, my shoulder aching with each lunge, and at last it bursts open. Brad is lying on the bed motionless. It takes me a moment to see the dark stain on the pillow, brownish at the edges but thick and black around his head.

When Melissa sees the hammer she tries to grab it, shouting something, but I shake her off, and the iron head crashes through the window. The room floods with wholesome air, and I stagger out into the hall and slump to the ground while Melissa bellows her disbelief. I know I should get the oxygen tank and share it with the others, but for a moment I don’t have the strength. I can feel the temperature dropping as the night air rushes into the stuffy house, and I just sit there, my back against the wall, breathing it in. I doubt it will save Brad.

Time passes. A minute or two, perhaps, but I’m still not thinking clearly and can’t be sure. But then I hear movement, and I look up to see a shadow in the stairwell. It shifts and turns into Marcus, looking dazed and unsteady.

“Jan?” he says. “What’s going on?”

“The generator,” I say, my head still foggy. “The exhaust was connected to a hose. We all have carbon monoxide poisoning. Keep breathing from the tank. And share it with the others.”

“What?” says Marcus. He looks even less focused than me, though whether that is the corrupted air he has been breathing or the high from the shot of pure oxygen I gave him, I can’t say.

“The tank in your room,” I say. “Get it. Use it.”

“I don’t understand,” says Melissa. She’s more alert than us, having only just come upstairs. Maybe her side of the house wasn’t affected since the hose ran right up the tower stairs.

“Help him,” I say. “Help them all.”

“I can’t tell if they’re breathing,” she says. “Brad’s head is all cut. I can’t tell if it’s bad, but there’s a lot of blood.”

“Give them the oxygen anyway. The ventilation is getting rid of the carbon monoxide from the air, but we have to get it out of their bloodstream.”

“I don’t understand,” says Marcus. “Why won’t they wake up?”

“It’s the gas,” I say vaguely.

“Will they be OK?”

“I don’t know, Marcus.”

“I don’t understand,” he says again.

I just sit and breathe, suddenly too tired to explain.