Cocaine stolen by family returning to prison (4)
I believe the answer is:
nick
'prison' is the definition.
(slang term for prison)
'cocaine stolen by family returning' is the wordplay.
'cocaine' becomes 'c' (drugs abbreviation).
'stolen by' is an insertion indicator.
'family' becomes 'kin' ('kin' can be a synonym of 'family').
'returning' is a reversal indicator.
'c' going into 'kin' is 'kcin'.
'kcin' backwards is 'NICK'.
'to' acts as a link.
(Other definitions for nick that I've seen before include "diabolical person's name" , "Prison - cut" , "Cop shop" , "Indent or slangily steal" , "Small boy" .)