The bike chain segment remained looped tight around my wrist as I stepped from the alley shadows. Midday traffic surged past the curb. Beside the mouth of the passage, an old municipal cast-iron storm drain grate lay set into the concrete curb, slightly tilted by cracked stone. I knelt down, pressing a gloved palm against the cold slotted iron. Deep beneath, water trickled in the dark. Taking the freed end of the bicycle chain, I threaded its final rusted link through the outer bar of the iron grate, driving a discarded square steel nail through the eyelet to lock it firm. Solid. Anchored to the curb, I held ground at the perimeter.