ObscureHollywood.net’s review published on Letterboxd :
Secret Service operative Jack Holt goes undercover to identify the mysterious leader of a gang of drug smugglers. Constance Cummings, whose father is murdered by the gang, helps him. Among the criminals are Boris Karloff, a murderous thug, and Edward van Sloan, a sinister doctor.
Weak in logic and continuity, but who cares, its fun in a loony sort of way. Especially dandy is the scene where van Sloan is preparing to carve up Holt, just for the fun of it.