Her momentum had knocked Patrick across the floor. He spun like a hockey puck over the tile, his mask and tank clattering with him. He wound up on his belly, facing me. We looked at each other.

“Sorry,” I said.

He mumbled something I couldn’t make out.

I scrambled over to the tank. The tube had been tugged to the very edge of the nozzle, a millimeter away from popping off. I secured it tightly and looked up. “You okay?”

He nodded, but I could see he was foggy. “‘Okay’ might be an overstatement.”

“We made a lot of noise, so we’d better move it before they get here,” I said.

I helped him up, and then we hustled back to the Respiratory Suite, Patrick hugging the hundred-pound H tank as he walked. He was having trouble moving well. I couldn’t count on his helping me much.

After we checked out the tanks—there were ten more big ones—I saw something in the back of the suite that spelled even better news. A beige machine the size of an industrial copier. Block letters on the side spelled out OXYGEN TANK FILL SYSTEM.

We now had a sustainable plan.

Whether we came back here for future missions or figured how to get the entire machine and its filters back to school, we had a way to keep him breathing.

With a simple push-button setup, the unit was surprisingly easy to figure out. It had a plug in the back but also a toggle for an internal backup generator, one of the benefits of emergency medical equipment. I inserted the lighter portable tank into the system and started filling it.

We wouldn’t have time to wait around.

“Can you carry another tank?” I asked.

Tucking the shotgun beneath his arm, Patrick swept up another tank with ease. Sometimes even I forgot how strong he was. I grabbed two tanks myself, staggering under the weight, struggling to keep them from dragging loudly on the floor. We hurried back into the hall.

Patrick led the way down the rear stairs, and I scrambled after him.

He shouldered through a door onto the ground floor, and we shot gazes up and down the corridor, but no Hosts were in sight. From the square we could still hear the scream of the ambulance siren. I prayed it had drowned out the commotion of our battle upstairs.

Sliding glass doors let out into an alley behind the hospital. “Let’s go,” Patrick said. “We can’t carry more than these.”

I looked frantically around the corridor, then saw what I was searching for up against a wall.

A gurney.

I ran over, heaving the heavy tanks onto the mattress. Patrick set his on there, too, then leaned on the railing with both hands, panting hard. Sweat ran from his hairline into his eyes as he struggled with the effects of the oxygen.