Julian leaned over, putting his face near the opening. He inhaled deeply, once, twice. His eyes widened slightly. “It… it smells like a car air freshener. Or vape juice. Did one of the subcontractors drop something down the wall?”
“Subcontractors finished eighteen months ago,” I said, my pulse quickening. “A spilled air freshener would have volatilized and dissipated within eight to twelve weeks. This is active. It’s generating heat or being replenished.”
I took the flashlight and laid my cheek flat against the plywood, shining the beam straight down the shaft.
The light cut through thirty feet of dead vertical space. Down near the mid-point—right where the ceiling of the first floor met the floor of the second—something glinted. It wasn’t the dull silver of galvanized ductwork, nor the brown paper of insulation.
It was metallic blue. Small. Cylindrical.
And beside it, taped directly to the exterior of the HVAC return duct, was a square black plastic housing with a tiny green light emitting a slow, steady pulse.
