Still feeling dizzy, I ran to add my weight to theirs. The metal unit looked like part of a giant air conditioner. I shoved myself against it and pushed. Seb was beside me – head down, hands propped on the metal edge as he groped for purchase with his feet. “Are you okay?” he gasped, glancing at me.

“I think so,” I said faintly. Alex’s eyes met mine and I could see the deep flicker of thankfulness in them; then he turned away without speaking as the metal unit scraped across the cement. The door burst open a few inches, then banged shut again as we all heaved. Incoherent shouts, a glimpse of angry faces.

“Oh god, they’re going to get through!” Liz’s cheeks were red with effort. “Alex, what are we going to do? There’s no place to hide up here!”

“Start pickin’ ’em off one by one as they come through,” grunted Sam on the other side of me. His broad shoulders looked like they had softballs in them as he pushed.

“Yes, that will work for about two minutes maybe,” said Seb, raising his voice over the shouts. The door was shuddering, shaking. “How many cartridges do you have?”

“Enough to make them sorry they ever followed us up here,” said Sam grimly. “I’m going down fighting, that’s all I know.”

“But we’ll still go down,” said Liz, sounding agonized. “There’s just too many of them! And Trish and Wesley—” She broke off with a sob. I felt like crying myself. Trish, who everyone had loved so much; Wesley, who’d wanted only to avenge his family. Were we supposed to open fire on them now?

The screams intensified as the door shoved open by almost a foot; we struggled to close it again.

“Okay, don’t panic,” said Alex. “We’ll have the advantage as they come through the door. We’re going to have to let go of the unit and position ourselves over to the side. When the crowd bursts through, start firing. Try a couple of warning shots first, but don’t waste too many cartridges if it doesn’t work.”

Though his tone stayed matter-of-fact, I knew how much he must hate this; he loathed the thought of using a gun against another human being. He wasn’t the only one. I imagined pulling the trigger; seeing someone crumple in front of me. My lips went dry. I didn’t think I could do it.

“Give me your gun and get behind me when we let go,” said Seb to me.

I swallowed. “Seb, no – I can’t let you shield me—”

His voice was strained. “Please, just do it. You don’t think you can shoot, and I can.”

“Seb’s right,” said Alex shortly. “Stay behind both of us.”