At the end of World War I, a division of the French Foreign Legion led by Major Foster (Gene Hackman) has been ordered to protect an archaeological expedition led by Marneau (Max von Sydow). The last expedition was destroyed along with its Legionnaire guards but Foster must follow orders... Meanwhile, Marco Segrain (Terence Hill), a part gypsy cat burglar who is on the run from the police, joins the Legion to escape arrest. He finds himself under the command of Foster, for whom he gradually acquires a grudging admiration.