The titular Marie-Louise is a young French lass who is evacuated to Switzerland when her country is overrun by the Nazis. Suffering a nervous breakdown, she is given comfort and shelter by a wealthy family. Unfortunately, living in the lap of luxury makes Marie-Louise hesitant to return home to her mother and war torn home. Eventually the girl comes to her senses, but it isn't easy.

If any one man is responsible for the rejuvenation of the postwar Swiss film industry, that man was director Leopold Lindtberg. Matto Regiert (Madness Rules) was co-adapted for the screen by Lindtberg from a novel by Friedrich Glauser. Heinrich Gretler stars as Police Constable Studer, the hero of several of Glauser's most popular works. This time, Studer must solve the murder of the director of an insane asylum -- and it's not (surprise, surprise) the most likely suspect, manic-depressive patient Herbert Caplaun. For box-office purposes, Matto Regiert stresses a romantic subplot involving Caplaun and nurse Irma Wasem.