Doc Levy (Roy Scheider) is an American secret agent who has been running interference between the US government and escaped Nazi war criminal Szell (Laurence Olivier). Believing that Doc has stolen a valuable cache of gems, Szell emerges from his South American hiding place and heads for New York. He has Doc killed, then kidnaps Doc's in-the-dark brother Babe (Dustin Hoffman). Repeating the phrase "Is it safe'" over and over, Szell, a onetime concentration camp dentist, tries to extract information from Babe by performing sadistic "oral surgery" upon him. Babe, who still doesn't know about the gems, escapes, breaking his own self-imposed rule of nonviolence to defend himself against his pursuers. The fox becomes the hound when Babe overpowers Szell and forces the old man to swallow his valuable diamonds. Marathon Man traces Babe Levy's progression from pacifistic naif to cynical street-smart scrapper.