What prisoner might long for, eh? (6)
I believe the answer is:
pardon
I believe this clue is a double definition.
'what prisoner might long for' is the first definition.
(a prisoner might want to be pardoned)
'eh?' is the second definition.
(both are used to ask someone to repeat themselves)
(Other definitions for pardon that I've seen before include "Polite expression of regret, please excuse" , "Forgive (an error)" , "Allow to go unpunished" , ""I'm sorry, could you say that again?"" , "Ask this to seek forgiveness" .)