“Malachi, do not touch the red button,” the controller responded. “Just hold the altitude pitch where it is.”

I stood back up and focused on the circuit breaker panel again.

My fingers traced the plastic collars until I found it: *AV-VENT-X*.

I gripped the black collar and pulled it outward until it clicked.

“I got it,” I told Miller. “I pulled the breaker.”

“Good,” Miller said, his voice faint through the static. “That should prevent the valves from opening automatically.”

“But Grace, we don’t know how much of the agent has already leaked through the seals.”

My stomach sank.

“What do you mean?” I asked.

“The seals on older Boeing models can degrade over time,” Miller said. “If the pressure in the cockpit is higher than the cabin, it will bleed through the bulkheads.”

I looked through the small glass window in the cockpit door.

The forward galley was empty, but the first-class cabin lay just beyond the blue curtain.

“I need to check on the passengers,” I said.

“Keep this phone line open,” Miller said. “Lay it on the center pedestal.”