Wary when star of US gangster movies drops in at last (5)
I believe the answer is:
cagey
'wary' is the definition.
(synonyms)
I don't understand the rest of the clue.
(Other definitions for cagey that I've seen before include "Keeping things to oneself" , "guarded" , "reluctant to give information" , "Secretive, cautious about giving information" , "not open" .)