 In February, 2001, Robert Hanssen, a senior agent with 25 years in the FBI, is arrested for spying. Jump back two months: Eric O Neill, a computer specialist who wants to be made an agent is assigned to clerk for Hanssen and to write down everything Hanssen does. O Neill s told it s an investigation of Hanssen s sexual habits. Within weeks, the crusty Hanssen, a devout Catholic, has warmed to O Neill, who grows to respect Hanssen. O Neill s wife resents Hanssen s intrusiveness; the personal and professional stakes get higher. How they catch Hanssen and why he spies become the film s story. Can O Neill help catch red-handed "the worst spy in history" and hold onto his personal life?