Abstract: A lock comprising a day bolt (1) and a night bolt (2), said day bolt (1) being urged by a spring (8) to an extended locking position and being retractable by a handle-operated tumbler (5) to a releasing position, said night bolt (2) urged by a spring to a retracted releasing position, and being lockable both in an extended locking position and in the retracted releasing position by a packet of tumblers (14) adapted to be swivelled by means of a suitable key to a position wherein the locking of the night bolt (2) is removed, thereby rendering it freely slidable.