Mischief maker first in prison after fraud (5)
I believe the answer is:
scamp
'mischief maker' is the definition.
(I've seen this in another clue)
'first in prison after fraud' is the wordplay.
'first in prison' becomes 'p' (1st letter of 'prison').
'after' is a charade indicator (letters next to each other).
'fraud' becomes 'scam' (scam is a kind of fraud).
'p' put after 'scam' is 'SCAMP'.
(Other definitions for scamp that I've seen before include "Tearaway" , "Rogue - perform inadequately" , "Troublemaker" , "Little Devil" , "villain" .)