Fixed charge to hold prisoner finally released (3,4)
I believe the answer is:
set free
'released' is the definition.
(I've seen this before)
'fixed charge to hold prisoner finally' is the wordplay.
'fixed charge' becomes 'setfee' (I've seen this in another clue).
'to hold' indicates putting letters inside.
'prisoner finally' becomes 'r' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'setfee' placed around 'r' is 'SET FREE'.
Can you help me to learn more?
(Other definitions for set free that I've seen before include "no longer detained" , "Clear" , "Turn loose" , "no longer confined" , "Uncaged birds have been" .)