“What is in that canister?” I asked, leaning closer to the tiny screen.

“It’s not carbon monoxide,” Nathan said, his hand finding mine in the dark.

His grip was incredibly cold.

“That’s liquid nitrogen.”

“They’re going to freeze the hydraulic lines of the door.”

On the screen, Julian began to attach the nozzle of the hose to the ventilation intake pipe above the door frame.

A thick, white cloud of super-cooled gas began to hiss from the connection.

“If those lines freeze, the locks will shatter,” Nathan said.

“And we won’t be able to open the door from the inside, even if we wanted to.”

Suddenly, the tiny screen in the safe flickered, and a new message popped up over the camera feed.

It was a local text document, written in a simple, unformatted font.

*Nathan, look at the bottom drawer of the safe. There is a second keyhole.*

*If you turn both keys at once, the fire suppression system will discharge.*

*But it will drain the remaining power in the room.*

*You will have five minutes of air left.*