Jim Parker will reveal the mischief-maker (3)
I believe the answer is:
imp
'the mischief-maker' is the definition.
(mischievous creature)
'jim parker will reveal' is the wordplay.
'reveal' says the answer is hidden in the clue.
'IMP' is hidden in the letters of 'jim parker will'.
(Other definitions for imp that I've seen before include "Small devil or sprite" , "Evil spirit" , "Goblin" , "old graft" , "A small mischievous devil" .)