Sgt. Mike Kincaid of the French Foreign Legion learns, from a Riff prisoner, that an attack will soon be made by the villainous Hussin on the Legion's outpost of Tarfa. Kincaid volunteers to lead nine other Legionnaires on a mission to delay Hussin's attack till reinforcements arrive. When he discovers that Hussin plans to marry Mahla, a girl from a rival tribe, in order to build a coalition against the French, Kincaid kidnaps Mahla. Hussin forcefully takes her back, but by now his planned attack on Tarfa is crumbling and Mahla has begun to fall in love with Kincaid.

Dick is faced with a series of brutal murders in which the victims, all from different social and economic backgrounds, are viciously slashed to pieces. Suspects abound but Tracy, getting a clue that there will be 15 murders in all, must find the common thread among the victims before more are killed.