The narrative centers on three brothers raised by their aunt at her country estate, though her husband’s financial dealings threaten their family's fortune. A significant amount of time elapses and the boys mature into men. Then a message requests that she have their final possession—the renowned "Blue Water" sapphire—appraised. She retrieves it from its secure location, but a power failure occurs, and the jewel disappears. The only people present were the young men and the butler, raising questions about who might be responsible. The following day, each of the brothers confessed to the theft and fled to enlist in the French Foreign Legion. They are assigned to an isolated outpost overseen by the harsh "Lejaune" (Noah Beery), who learns of the stolen jewel and intends to steal it from whichever brother possesses it... It's a well-designed plot, despite the fact that we, as viewers, have a strong suspicion about what transpired. There remains a sense of danger as their experiences in the desert—confronting their merciless sergeant, enduring the heat, and facing raiding tribesmen—escalate quickly. While Ronald Colman ("Beau") is nominally listed first, he, along with his on-screen brothers Neil Hamilton ("Digby") and Ralph Forbes ("John"), share the responsibility of propelling this thrilling adventure forward at a brisk tempo, featuring ample action and impressive visuals (though filmed in Arizona rather than Morocco). Subsequent film adaptations have been numerous, but none quite measure up.

Source on TMDB