Work hard to reveal corruption (5)
I believe the answer is:
graft
I believe this clue is a double definition.
'work hard' is the first definition.
(graft can mean to work very hard)
'corruption' is the second definition.
(I've seen this in another clue)
'to reveal' acts as a link.
(Other definitions for graft that I've seen before include "Surgical transplant" , "Hard work - corrupt profit" , "Hard work - swindle" , "Means of propagation - hard work?" , "Transplant - hard work" .)