Secrets of the French Police ★★★

A series of murders, including of an undercover policeman, has baffled the Sûreté (French Police). Gwili Andre, a flower seller, is kidnapped. Gregory Ratoff, who is impersonating a Russian nobelman, subjects Andre to extreme distress to force her to believe that she is
Anastasia Romanoff. Ratoff plans to use the false Anastasia to claim the Romanoff fortune that is held by Russian fugitives around the world. Ratoff and his thugs have been killing anyone in Paris who has knowledge about Anastasia or who knows Andre. Police Detective Frank Morgan investigates the deaths and the disappearance of the flower seller.

This is a fun film of the grand Guignol type. Besides murders and impersonations, there is a mysterious chateau in which Ratoff turns his discarded women into bloodless (literally) plaster statues.

Frank Morgan has a straight role as the principle investigator of the crimes.