In Marseilles, gunrunner Jacques Morrell murders an archaeologist and takes his identity to travel to North Africa; supposedly working on a dig in a Foreign Legion base he is ideally placed to plan his next scheme. Duval is called in to investigate the hijacking of arms supplies, and becomes suspicious of the visiting Professor; he also discovers Morrell's source of information within the Legion, Corporal Kahn. Too late to prevent the last hijacking, he finds Morrell has killed his now-useless contact - news Duval is able to use to persuade Kahn's lover to help him.