A multipoint mortise lock assembly includes an extended face piece mounted flush along the edge of a door, a mortise lock connected to the face piece, and a pair of hook bolt latch mechanisms mounted to the face piece above and below the mortise lock. An elongated actuator, which is preferably a flat rod slidingly mounted to the back of the face piece, acts to extend and retract the hook bolts in synchronism with a deadbolt in the mortise lock. The actuator is connected between a deadbolt arm in the mortise lock, which drives the deadbolt, and the hook bolt latch mechanisms. The deadbolt arm is driven conventionally, such as by a key or a thumb latch, and the design allows one hand operation of the multipoint mortise lock assembly.