Based on the novel by Philip MacDonald, a British patrol in the desert is killed one by one by unseen Arabs.
In 1917 in Mesopotamia British troops are fighting the Arab enemy. In the desert a patrol's officer is killed by a sniper. His body is buried. Sanders (Boris Karloff) prays but is cut short by the sergeant (Victor McLaglen). The sergeant says they have no orders and are lost but will head north toward the river. The patrol with about a dozen men arrives at an oasis. The sergeant assigns Pearson (Douglas Walton) to sentry duty but is able to sneak up on him. Pearson tells him how he ran away to enlist and how his mother cried. In the morning the sergeant finds Pearson knifed in the back, and the horses are gone. George Brown (Reginald Denny) talks about Malayan girls, and the religious fanatic Sanders preaches to him. Brown believes in the futile war and killing Arabs. The sergeant tells his men they must stay there and hope for relief. One man climbs a palm tree to see and is shot.
McKay (Paul Hanson) and Cook (Alan Hale) head north to get help. The sentry Abelson staggers on the dunes and is shot. The bodies of McKay and Cook are found returned with their eyes mutilated. Sanders tells the sergeant that Brown left to hunt Arabs by moonlight. An airplane flies over and lands; but the pilot does not hear warnings to take cover and is soon shot. Sanders accuses the sergeant of killing him and is tied up. The sergeant and Morelli (Wallace Ford) go to the plane and get its machine gun. The sergeant sets the plane on fire. A British patrol sees the flames from a distance. Sanders gets loose, walks out with a cross, and is shot. Morelli, afraid of being alone, goes after him and is shot running back. The sergeant, now alone, buries them and marks the graves with swords. Arabs approach, and the sergeant shoots them with the machine gun. He laughs and is shot at, but he kills the last Arab with a rifle. The British patrol arrives, and its officer asks the sergeant where his men are. He points to the row of swords in the sand. In the final scene the soldiers march off.
This bleak story exposes the futility and waste of war and the killing of enemies. Instead of offering consolation or understanding, a religious fanatic gets on the others' nerves. The sergeant doesn't know where they are going nor why. The enemy is unseen until the end when they are all killed, emphasizing the mysterious dehumanization of war.