Chuck Connors and Jimmy Barton are two American soldiers charged with guarding a scientist in a remote Siberian town. The friends find themselves at odds when they both fall under the spell of Sonia, a disgraced Russian princess. Unbeknownst to them, Sonia is a spy sent to steal the scientist's latest invention. Duty will have to overcome jealousy if Chuck and Jimmy are to prevent the deadly weapon from falling into enemy hands.
Three Legionnaires is the last screenwriting credit for Carl Harbaugh, Hal Roach's top gag writer in the 1920's. In addition to writing countless shorts for Roach, Harbaugh wrote the scenarios for the Buster Keaton features College (1927) and Steamboat Bill, Jr. (1928). Leading man Lyle Talbot was extremely familiar to 1930s audiences from his appearances in pre-Code crime melodramas such as Three on a Match and 20,000 Years in Sing Sing (both 1932). His career would take a downturn into movie serials and Ed Wood films before being cast as Joe Randolph on the popular TV series The Adventures of Ozzie and Harriet (1956-1966). Co-star Robert Armstrong is best remembered for his role as entrepreneur Carl Denham in King Kong and its sequel Son of Kong (both 1933). Often billed as "The French Bombshell", actress Fifi D'Orsay plays a Russian temptress, though her French accent remains intact.