Based on a character created by Michael Arlen
The Falcon was said by some to have been created in a magazine short story in 1940 (but was he?) and made his way to the big screen with little delay, in 1941. A Date with the Falcon came along the next year and before the decade was out sixteen movies of his adventures had been made. I have to read or view any of the exploits of The Saint, a popular character who predated The Falcon, but they were apparently similar enough to spawn at least one lawsuit.
George Sanders, who took the role of The Falcon in the first few installments had also played The Saint a number of times - imagine that - and for my money he resembles yet another serial character who was quite popular in this era - The Lone Wolf. Like that character The Falcon is a rather cultured and debonair sort, though I wasn't able to discern whether he had a dubious past like the Wolf, a reformed jewel thief. Other similarities include that tried and true device of the comic relief sidekick.
And it's jewels that are at the heart of this movie, now that you mention it, specifically artificial diamonds that an enterprising scientist has created in his lab. Before long a few bad eggs decide they want to get in on things and the scientist proceeds to disappear. At which point police inspector O'Hara beseeches and badgers The Falcon to help make sense of it all. O'Hara is played by James Gleason, by the way, who plays essentially the same role (the flustered, blustery cop) that he did in the Hildegarde Withers movies and everything else I've seen him in thus far.
Well, The Falcon manages to crack the case in due course - would you really expect anything less? But not before a merry series of events unfolds that border on slapstick at times and which find him repeatedly falling into the clutches of the baddies and then escaping, as well as getting in hot water with O'Hara and not the least of all, his jealous fiancée.
Which sounds a helluva lot like several of the Lone Wolf reviews I've written. Here's a contemporary review from the New York Times and a good overview of the character's "life" in its various media incarnations.