Unusually adult in tone, this excellent Hopalong Cassidy Western features Gwen Gaze as Lorna Drake, an aristocratic British girl and Hoppy's new employer. When Cassidy (William Boyd) refuses to be ordered about by the supercilious lady, Lorna has him arrested for horse stealing. The dumbfounded sheriff (Earl Hodgins) is even more puzzled when Miss Drake turns right around and demands that Hoppy be released into her custody. Although obviously smitten with the strapping foreman, Lorna cannot curb her ingrained haughtiness, and the two come to verbal blows more than once. Meanwhile, the girl's former fiancé, the foppish Ronald Harwood (John Warburton), becomes an easy target for Hoppy's nemesis, former prison inmate Scar Lewis (Al Bridge). With Harwood's help, the latter concocts a plan to ambush the man who sent him up the river. Based on Clarence E. Mulford's 1918 The Man from Bar-20: A Story of the Cow-Country, Partners of the Plains came complete with a song, Ralph Freed and Burton Lane's "Moonlight on the Sunset Trail," performed by leading lady Gwen Gaze. The Western was filmed on location in the San Jacinto National Forest.