Acoustic Reconnaissance

I advanced further along the corridor baseboard toward the heavy fire door marking the stairwell entrance. At floor level, a slight draft pulsed rhythmically beneath the steel slab. I unslung my rifle to free both hands, kneeling close to the threshold to press my gloved palm against the cold metal jamb. Deep vibrations traveled down the internal shaft—echoes of descending steps and metallic latches clicking floors away. Finding a discarded brass safety pin near the corner molding, I wedged it into the base of the rubber door gasket to prop open a millimeter-wide listening slit. The stairwell offers a viable vertical route.