Doc Levy (Roy Scheider) is an American secret agent who has been running interference between the U.S. 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 and gearing up for sadistic revenge.