Notorious outlaw Lawrence Grey has been captured near El Paso. Marshal Neilan has a proposal for him. Neilan will set Grey free if he tries to locate John Ray, a man who was last known to be living in San Vicente, Mexico. The men Neilan sent previously have disappeared or quit the job. Brick Forbes of Pittsburgh is worth millions. Ray once did him a kindness. Now that Forbes is desperately ill, he wants to leave his fortune to Ray rather than to his own relatives.

Grey agrees to Neilan's proposal and goes to San Vicente, where he promptly saves the life of Mexican general Miguel O'Riley during a bombing attempt. The general makes inquiries and learns that the stranger who saved his life is called John Lawrence and that he is studying Spanish. Another American named Dickson Jarvis, employed by Forbes's relatives, informs O'Riley that Lawrence is actually a wanted outlaw on both sides of the border. Later, Jarvis is murdered. Lawrence has his own audience with General O'Riley and asks him for a guide into the mountains. O'Riley sends for Oliver Slade, a man who strangely resembles the one who killed Jarvis. This proves only the beginning of an intrigue in which Lawrence's life is threatened continually from all sides.