During the First World War, a group of British cavalrymen are stranded in the Mesopotamian Desert. The only officer in the group who knew their location, destination, and orders is killed by an Arab sniper. The veteran sergeant (played by Victor McLaglen) takes charge. After they set up camp at an oasis, Arabs kill one sentry and steal their horses. The soldiers find themselves surrounded by unseen enemies and are picked off one by one by snipers. When two soldiers try to go for help, their bodies are returned, murdered. Only three remain: Morelli (played by Wallace Ford), the sergeant, and Sanders (played by Boris Karloff), a religious fanatic.
A rescue plane flies over, but the pilot is killed after landing. Sanders goes insane and makes a makeshift cross and sets out across the desert. Morelli chases after him, but both are shot. The sergeant is left alone and holds off the attacking Arabs with a machine gun until a rescue party arrives.