Troublemaker out of prison finally for impeccable behaviour (7)
I believe the answer is:
stirrer
'troublemaker' is the definition.
(I've seen this before)
'prison finally for impeccable behaviour' is the wordplay.
'prison' becomes 'stir' (informal term for prison).
'finally' suggests the final letters.
The final letters of 'for impeccable behaviour' are 'rer'.
'stir'+'rer'='STIRRER'
'out of' is the link.
(Other definitions for stirrer that I've seen before include "engineering several revolutions in Darjeeling?" , "One making solution perhaps" , "Troublesome" , "Troublemaker (informal)" , "One deliberately causing trouble" .)