Beg to get freed finally in prison (5)
I believe the answer is:
cadge
'beg' is the definition.
(cadging is a kind of begging)
'freed finally in prison' is the wordplay.
'finally' says to take the final letters.
'in' is an insertion indicator.
'prison' becomes 'cage' (I've seen this before).
The final letter of 'freed' is 'd'.
'd' inserted inside 'cage' is 'CADGE'.
'to get' acts as a link.
(Other definitions for cadge that I've seen before include "Scrounge, sponge" , "beg" , "Scrouge, ask for" , "freeload" , "Try to borrow" .)