Do "unlock a mystery" and "solve a mystery" mean the same thing?
Important Poems It also has clues that help and clues that don't really help, but all clues help solve a mystery.
I would use 'unlock' only if the metaphor fit. That is, if a 'key' piece of the puzzle is missing and once found the mystery is solved, then 'unlock' is a good term.
'Solving' generally implies a series of contributory steps, not just one crucial one.