In "Sinister Journey," Hopalong Cassidy (William Boyd) and his sidekick California Carlson (Andy Clyde) go undercover as railroad workers to investigate a series of mysterious accidents and acts of sabotage in a railroad yard. Suspicion initially falls on the owner's estranged son-in-law, Lee, but Hoppy discovers the real culprits are trying to frame Lee while also exploiting the existing animosity between him and the owner for their own criminal ends.