Abstract: A lock housing is adapted to be mounted at the free vertical edge of the inactive one of a pair of hinged doors that have adjacent vertical edges when both doors are closed. Slidably mounted in the housing is an axially movable shaft that extends vertically therefrom and has a normally retracted latch bolt mounted on its outer end. Operatively connected to the opposite end of the shaft is the inner end of a rocker arm, the central part of which is pivotally connected to the housing on a horizontal axis. A cam pivotally connected on a vertical axis to the housing normally projects from it for engagement by the free vertical edge of the active door for swinging the cam into the housing to swing the rocker arm vertically in order to project the latch bolt from a horizontal edge of the inactive door. The rocker arm is so mounted in the housing that it will be moved by the cam bodily away from the free edge of the door if the shaft cannot move, whereby the mechanism will not be damaged.