That’s when I hear the shouts. I leap down and sprint to the wall. A Recruiter stands outside the headquarters, pointing up at us as if trying to figure out what’s going on. As the balloon lifts higher behind me he turns and runs back inside and before long there’s a stream of them racing toward our building.

“Go!” I shout at Elias. “They’re coming!”

My sister’s face pales as she joins Elias by the fire, fanning the smoke into the bag as hard as she can. It raises from the ground but not enough to carry the weight of the basket and us.

“They’re at the door downstairs,” I yell.

“It’s not going to fill in time,” Elias mutters under his breath and my sister knocks him with her elbow, telling him to shut up.

I look around the roof, searching for anything to buy us time. We’d used melted fat to coat the fabric and still have a vat of that and a few bags of oil for the lanterns. I grab them both and drag them to the stairwell.

In the center of the roof the envelope’s filling, the seams starting to strain and the basket lifting more. I can already hear the Recruiters shouting as they spiral up the steps. We’re running out of time.

Collecting pieces of fabric and wood, anything we won’t need anymore, I throw them all into the stairwell and then light the bag of oil and toss it down after. There’s a concussion and whoomp of air as the oil ignites, spreading along the steps and eating at the walls, bathing the hallway in flame. I slam the door.

“I guess you weren’t planning to need those stairs if this didn’t work,” Elias grouses as he lifts my sister into the box. She starts to stoke the fire in the center cauldron.

“It’s not going to burn long,” I tell him. There’s the sound of something popping and a high-pitched sucking sound as below us one of the windows explodes. I can’t help cringing, thinking about the awful waste of the destruction.

“Let’s go,” Elias says, holding out a hand to me. I let him help me into the box and the balloon jerks us from the roof, Elias still lifting his leg over the side.

The balloon struggles at first, skimming across the roof, and then it pulls free and hovers, dragging us up into the air as the door to the stairwell slams open and flames leap out. Men in black uniforms chase us on the ground, but we’re rising higher and higher and their sounds are lost to the wind. Elias points us toward the river, trying to clear the airspace over the Sanctuary as Recruiters scramble for crossbow bolts.