Thomas "Babe" Levy, portrayed by Dustin Hoffman, is a dedicated Ph.D. candidate in history with a passion for marathon running. He spends his days delving into the shadows of his family's past, particularly the suicide of his father, who fell victim to the fierce Communist witch hunts during the notorious Joseph McCarthy era. Unbeknownst to him, his brother, Henry James Levy—referred to as "Doc" and played by Roy Scheider—is not merely an oil company executive as he claims, but a U.S. government agent linked to a secret agency led by Director Peter Janeway, portrayed by William Devane.
As Doc plays the role of the ever-busy businessman, he frequently travels under the pretense of work. His life intertwines dangerously when a key to a safety deposit box linked to a Nazi war criminal becomes a target of sinister forces. This leads to an unexpected twist when a violent encounter results in the death of the criminal's brother in a traffic accident after a heated argument with a frustrated Jewish American motorist.
Doc harbors urgent suspicions about the impending arrival of the notorious Dr. Christian Szell, played impressively by Laurence Olivier. With a plan set in motion, it becomes a race against time as Babe unwittingly finds himself in a romance with the enchanting Elsa Opel, embodied by Marthe Keller, who initially presents herself as a Swiss national. However, their relationship takes a dark turn when they are mugged one night, an event that deepens the mystery surrounding Elsa’s true background.
Over lunch, Doc cleverly extracts information from Elsa, realizing there may be hidden ties to Szell, yet he only passes on that she is seeking marriage for a green card. When Szell arrives on American soil, Doc takes it upon himself to confront the war criminal, warning him to stay away from Babe. The confrontation takes a deadly turn when Szell fatally wounds Doc, who manages to stagger back to Babe's apartment, collapsing in his brother's arms without revealing crucial secrets.
Babe soon finds his life spiraling out of control as inquisitive police detectives and government agents, led by Janeway, interrogate him about his brother's mysterious final words. As events escalate, Babe is captured by Szell's brutal henchmen. Within an infamous and chilling scene, the skilled dentist Szell tortures Babe, repeatedly asking, >"Is it safe?" Believing he can withstand the torture, Babe remains steadfast in his ignorance and eventually loses consciousness.
Rescue comes in a twisted form as Janeway saves Babe, only to reveal his duplicitous nature as a double agent colluding with Szell. Babe is thrown back into the clutches of the very monster he hoped to escape from. Szell's intentions come to light—he seeks information about the diamonds he looted from his victims during the Holocaust, creating a tense atmosphere as he questions Babe's loyalty to Doc and his knowledge of the criminal's activities.
Eventually, in a bid for survival, Babe produces a risky plan: he lures Janeway and Szell’s men to attempt an ambush, taking them by surprise. The scene intensifies as Janeway's ambitious betrayal leads to violence, and Babe finds himself believing that revenge might be possible. Szell's desperate attempts to reclaim his riches lead him into a chaotic situation where paranoia drives him to brutality.
In a gripping climax set against the backdrop of New York's vibrant streets, Babe confronts Szell, forcing him into a harrowing ultimatum regarding his fortune. Rather than deliver a fatal blow, Babe challenges Szell to swallow as many diamonds as he can to prove his worth. However, after a tense standoff that ends in physical confrontation, fate takes a fatal turn for Szell, leading to a moment of poetic justice as Babe retrieves his gun and jettisons it into the depths of the Reservoir, symbolizing a powerful act of liberation from the haunting legacy of his past.
