Thief, one's partner, say, taking lead from hellraiser (10)
I believe the answer is:
shoplifter
'thief' is the definition.
(shoplifter is a kind of thief)
I can't explain the rest of the clue.
(Other definitions for shoplifter that I've seen before include "guilty party" , "Thieving customer" , "A petty criminal" , "Criminal (in a retail context)" , "Robber" .)