Through the Flap

The metal passage narrowed. Ahead sat a hinged damper flap, shut tight across the duct. I tapped it with my knuckles. Hollow clang. I wedged my fingers into the lower seam and heaved upward. The hinge groaned, then clicked into a locked notch overhead. Cool air rushed across my face. On the other side, a square junction opened up with thick cables tied in neat bundles. I hopped over the sill and set down my green device. Clear ground. No obstacles left in this branch.