A lock. The lock includes an inner handle assembly, a latch bolt, and an outer handle assembly. The outer handle assembly includes an outer handle, an outer spindle, an actuating sleeve rotatably mounted in the outer spindle and having two guide slots each having an inclined section and a horizontal section, a locking plate mounted in the actuating sleeve and including two wings, and an unlatching member operably connected to the latch bolt. Each wing is extended through an associated guide slot into an associated positioning slot in the outer spindle. When the lock is in an unlocked state, the unlatching member is engaged with the locking plate to allow joint rotation. When the lock is in a locked state, the unlatching member is disengaged from the unlatching member such that the unlatching member is not turned when the outer handle is turned.