A prospector is murdered by The Cactus Kid and his gang, who hope to find the murdered man's goldmine. The miner's dog, Rin-Tin-Tin, recognizes the killers, who thereafter seek to use the dog to locate the lost mine. With the help of a government agent and a young girl, Rinty saves the mine and brings the bad guys to justice.
Unfortunately the movie The Lone Defender is not yet available on HBO Max.
| Directing | Richard Thorpe | Director |
| Writing | William P. Burt | Screenplay |
| Writing | Bennett Cohen | Screenplay |
| Writing | Harry L. Fraser | Screenplay |
| Production | Nat Levine | Producer |
| Editing | Wyndham Gittens | Editor |
| Crew | Joe Bonomo | Stunts |
| Crew | Kermit Maynard | Stunts |
| Crew | Arthur Metzetti | Stunts |
| Crew | Victor Metzetti | Stunts |
| Camera | Benjamin H. Kline | Director of Photography |
