Where order is kept to release criminal at first (7)
I believe the answer is:
convent
'where order is kept' is the definition.
(as in an order of nuns)
'release criminal at first' is the wordplay.
'release' becomes 'vent' (vent can mean to release or let out).
'criminal' becomes 'con' (abbreviation for 'convict').
'at first' means one lot of letters go next to another.
'vent' after 'con' is 'CONVENT'.
'to' is the link.
(Other definitions for convent that I've seen before include "Community of nuns" , "Religious house" , "Religious community" , "Building for prayer" , "Nunnery" .)