The Squeeze (1987)

His ex-wife asks the unsuccessful gambler and inventor Harrison for a small favor: to get her a parcel from a friend's apartment - without telling him what's in it. Suddenly he finds himself assaulted by villains and shortly after even under suspect of murder. The inexperienced P.I. Rachel is hired by an unknown party to rid him of the parcel - but soon befriends him. Together they try to figure out what kind of game is being played.