It's early 2001 and Eric O'Neill (RYAN PHILLIPPE) is employed by the FBI with dreams of becoming an agent. He gets the chance when supervisor Kate Burroughs (LAURA LINNEY) picks him for an assignment that could be one of the most important in the agency's history.
That's because the powers-that-be believe that veteran agent and computer expert Robert Hanssen (CHRIS COOPER) is actually working as a double agent for the Russians. Kate also informs Eric that Robert is a sexual deviant, thus making the young man unsure of what to expect on his first day working for the 56-year-old veteran who's been made head of the fictitious Information Assurance Division.
Robert comes off as cold and calculating, and untrusting of his supervisors. Yet, his strong religious convictions and family ties to his wife Bonnie (KATHLEEN QUINLAN) and their kids make Eric second-guess the assessment made by Kate as well as fellow supervisors Rich Garces (GARY COLE) and Dan Plesac (DENNIS HAYSBERT).
To make matters worse for Eric, he can't tell his wife Juliana (CAROLINE DHAVERNAS) about his real assignment, a fact that leads to tension between them, especially when Robert and Bonnie infiltrate their lives, pushing their religious beliefs on them. From that point on and despite his doubts, Eric tries to note and collect any sort of incriminating evidence against Robert, all while trying to prevent his new boss from discovering what's occurring.