Fresh plot twist involving a thief (10)
I believe the answer is:
shoplifter
This clue might be a double definition.
'fresh plot twist' is the first definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'a thief' is the second definition.
(shoplifter is a kind of thief)
'involving' is the link.
(Other definitions for shoplifter that I've seen before include "Thieving customer" , "A petty criminal" , "Thief" , "guilty party" , "Robber" .)