Though running a mere 75 minutes, Rio has enough plot for ten movies. Basil Rathbone and Sigrid Gurie, previously teamed in The Adventures of Marco Polo, head the cast as crooked French financier Paul Reynard and his wife Irene. Sentenced to a ten-year term in a French penal colony for bank fraud, Paul wonders if his wife will remain faithful to him. At first glance it seems that he has nothing to worry about: Irene and family friend Dirk (Victor McLaglen) head to Rio to arrange for Paul's escape, with Dirk vowing to shield Irene from any and all sexual predators. But once she's landed in the Brazilian capital, Irene falls in love with red-blooded American engineer Bill Gregory (Robert Cummings). Upon emerging from his dank prison cell, Paul realizes that he's lost his wife forever to a better man. Seeking revenge, he prepares to shoot Bill in cold blood, but good old Dirk intervenes, paving the way for a happy ending -- for everyone but Paul, that is. Though he plays a thoroughly unsavory character, Basil Rathbone ends up the most sympathetic person in the film, and as such he's the only real reason to sit through the melodramatic convolutions of Rio.
by Hal Erickson synopsis