Abstract: The disclosure relates to a locking cylinder and a key therefor. The locking cylinder has a flat slide plate and at least one pin tumbler for selectively engaging a corresponding recess in a key inserted into the lock. Insertion of the proper key which results in displacement of the pin tumbler allows longitudinal sliding movement of the flat slide plate within the cylinder lock. Sliding movement of the flat plate aligns the side edges of the flat plate with side bar pins so that, following such longitudinal displacement, the body of the cylinder can be rotated relative to its housing to effect a locking or unlocking of the lock mechanism.