Arsène Lupin Returns with Melvyn Douglas, Warren William, and Virginia Bruce. Cocksure G-man Steve Emerson (Warren William) has been making headlines with his gun-blazing gang busting. At the height of his fame, he decides to move on to the more lucrative career of insurance detective. His very first case is to investigate the near-theft of the de Grissac emerald. Count de Grissac, his niece Lorraine (Virginia Bruce), and cousin have been robbed in their hotel room but the thief mistakenly took a replica of the emerald. Clues in the room point to the famed gentleman thief of France, Arsène Lupin, who has been presumed dead. The de Grissac family return to France, accompanied by Emerson.
Upon arrival in France, they are met by Rene Farrand (Melvyn Douglas), who is Lorraine's wealthy suitor (much to Emerson's chagrin). While Farrand and Emerson vie for Lorraine's affections the de Grissac emerald is stolen, successfully this time, from the family safe. On the safe is the identifying mark of Arsène Lupin, by which I mean Lupin has signed his name. Not too subtle, this Lupin.
But we have learned that Farrand is actually the real Lupin but has gone straight. So who is committing these crimes and implicating Lupin? Emerson suspects that Farrand is Lupin, and Farrand must prove his innocence without admitting he used to be Lupin. And both men must try to make time with Lorraine.
Arsène Lupin, gentleman burglar, is a character from a series of French mysteries contemporary to and compared to the Sherlock Holmes stories. There was an earlier Arsène Lupin movie from MGM with John and Lionel Barrymore, hence the "returns". The male leads carried this movie with both characters being suave and confident, but with Emerson as the American tending more to brute force and bravado and Farrand the European more to cleverness and trickery. In one scene, to impress Lorraine, Emerson does hand stands and tears a phone book while Farrand does slight of hand with playing cards and coins.