One to leak information and reveal all (9)
I believe the answer is:
singleton
'one' is the definition.
(singleton is a kind of one)
'leak information and reveal all' is the wordplay.
'leak information' becomes 'leton' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'and' is a charade indicator (letters next to each other) (I've seen this in other clues).
'reveal all' becomes 'sing' (sing can mean to confess or inform the police).
'leton' put after 'sing' is 'SINGLETON'.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for singleton that I've seen before include "could be ace on its own?" , "Bachelor maybe" , "spinster or bachelor?" , "One of a kind" , "Eg lonely heart" .)