John has fled to the Foreign Legion in search of his missing brothers. At the Legion recruiting office in Paris he hears news of them and encounters the sinisterly friendly Boldini.

Reunited in the Legion, the Geste brothers have made two good friends, the Americans Hank and Buddy, and one dangerous enemy-the sadistic and tyrannical Sgt-Major Lejaune.

Sergeant-Major Lejaune now believes Beau is carrying a valuable jewel, and is determined to have it. A first attempt at theft is a failure. Then Lejaune announces that the squad is to be posted to Fort Zinderneuf, where the Geste brothers will be in his power.