Unlock to reveal (8)
I believe this clue is a double definition.
'unlock' is the first definition.
'reveal' is the second definition.
(disclosing is a kind of revealing)
'to' acts as a link.
(Other definitions for disclose that I've seen before include "Lay bare", "Divulge or expose", "Uncover", "Reveal, expose to view", "Divulge, reveal".)