A downhole apparatus comprises a piston mounted within a bore and being reconfigurable from a lock configuration to an unlock configuration in response to a pressure sequence applied within the bore. When the piston is in its lock configuration, a lock is supported by the piston such that the lock partially extends into the bore and engages a lock profile of the piston to restrict movement of the piston in a first direction towards its unlock configuration. In response to a first event of the pressure sequence, the piston is moveable in a second direction to desupport the lock and permit the lock to be wholly received into the bore and allow the piston to move in the second direction towards its unlock configuration in response to a subsequent event of the pressure sequence.