Eric O'Neill is a young ambitious FBI employee assigned to work undercover as a clerk to Robert Hanssen, a senior agent he is told is suspected of being a sexual deviant.

He frequently rails against the bureaucracy of the FBI and complains that only those who regularly "shoot guns" are considered for senior positions instead of those, like himself, who are involved in vital national security matters.

She admits that the sexual deviance allegations are only a secondary consideration and that Hanssen is suspected of having spied for the Soviet Union and Russia for years and being responsible for the deaths of agents working for the United States.

The entire Information Assurance Division that Hanssen now heads was created specifically to lure him away from his previous job as liaison to the State Department, and his office was specially constructed with hidden surveillance equipment.

O'Neill is ordered to obtain data from Hanssen's Palm Pilot and keep him occupied while FBI agents search his car and plant covert listening devices in it.

Among the major changes made for the film: O'Neill's memoir about the Hanssen case, Gray Day: My Undercover Mission to Expose America's First Cyber Spy, was published by Penguin Random House in Spring 2019.

The site's critics consensus reads, "Powered by Chris Cooper's masterful performance, Breach is a tense and engaging portrayal of the FBI's infamous turncoat.

Manohla Dargis of The New York Times said, "One of the strengths of Breach, a thriller that manages to excite and unnerve despite our knowing the ending, is how well it captures the utter banality of this man and his world.