James Garner plays a frontier scout who, while seeking revenge on the murderer of his Comanche wife, rescues Andersson from the Apaches and returns her to her husband (played by Weaver). He joins an army unit bringing supplies to the fort. Poitier is the horse breaker attached to the group. All hell breaks loose when the Apaches pin them down far from aid. This is a traditional-type Western with interesting actors. I enjoyed watching it, even on TV with commercials.
DVD Talk reviews the Kino Blu-Ray release, calling the story "average" but worth seeing for Garner and Poitier's work together, and saying that "one waits for something cool to happen and it never seems to." The Spinning Image says, "the action is plentiful, the politics not battered over the audience's heads, and Duel at Diablo a solid effort without being stodgy".