Your standard "infiltrating the organization" noir, a la Loan Shark and the like. There's not a whole lot of finesse to this cheapie flick, the performances are pretty flat and the dialogue is nothing special, but it's got an intriguing layer of sleaze over it, including Frank "The Riddler" Gorshin as a creepy, leering pedo. There's a couple of other interesting touches (the acid, throwing Gorshin under a train) but mostly it's rather formulaic and forgettable.