Abstract: A latch mechanism for a patio door having a narrow rectangular frame surrounding a window and slidable in a casing so that a vertical frame side abuts the casing when the door is closed. A pair of vertically spaced keepers on the casing are engagable by a pair of spaced latches on the door frame. The latches are biased toward an open position, and are moved by the keepers to a latching position when the door is closed. Catches secure the latches in the latching position, and the door handles are operably connected to the catches by a pair of longitudinally movable tie bars and pivoting links. A locking cam gear is movable by a sliding rack actuator between an unlocked position clear of the tie bars and a locked position with a raised cam surface engaging the tie bars to prevent longitudinal movement of the tie bars.