Prisoner at home with companion (6)
I believe the answer is:
inmate
'prisoner' is the definition.
(inmate can mean someone in prison)
'home with companion' is the wordplay.
'home' becomes 'in' ('he's home' can mean 'he's in').
'with' is a charade indicator (letters next to each other).
'companion' becomes 'mate' (both can mean a friend).
'in'+'mate'='INMATE'
'at' acts as a link.
(Other definitions for inmate that I've seen before include "Occupant" , "One is confined to an institution" , "eg Prisoner" , "Lag" , "One living in (prison)" .)