Pierre Gilieth has murdered a man in France, and escapes to join the Spanish Foreign Legion. One of the soldiers he meets and becomes friends with is Fernando Lucas who is really a member of the secret police whose goal is to trap Gilieth into admitting his guilt. Gilieth also falls in love with and marries Aischa la Slaoui, an Arabian dancing girl. Gilieth and Lucas, now mortal enemies, are the last two survivors of a desert outpost under siege by Riff soldiers. The troop commandant, before he dies, makes Lucas realize that Gileith has more than expiated his crime back in France by his heroism under fire.