ObscureHollywood.net’s review published on Letterboxd :
A thief is determined to steal the famed ruby necklace belonging to the Count de Grissac, and he seems to be famed gentleman thief Arsene Lupin who the French police thinks is dead. American detective Steve Emerson is trying to catch the thief and prevent the theft of the jewel. Rene Farrand, actually Lupin himself, wants to find the man impersonating him. Farranc loves Lorraine de Grissac, the niece of the owner of the jewel.
A sequel to the 1932 film Arsene Lupin, Arsene Lupin Returns has a complex plot involving multiple suspects, including Farranc and Emerson, the real jewel and a copy, several robberies and murders. Melvyn Douglas playing Lupin and Warren William as Emerson are both featured and have nearly equal screen time.