In the early 1970s, Mark Felt, the Deputy Associate Director of the FBI, finds himself navigating a tumultuous political landscape following the sudden death of his boss, J. Edgar Hoover. Despite his extensive experience and loyalty to the Bureau, Felt is overlooked for the position of director, which goes to the politically amenable L. Patrick Gray. Soon after, the FBI is tasked with investigating a break-in at the Democratic National Committee headquarters at the Watergate office complex. Suspecting a deeper conspiracy connected to the White House, Felt faces mounting pressure from both the new leadership and external forces to curtail the investigation.

As Felt grapples with his allegiance to the Bureau and his understanding of justice, he initiates secret meetings with journalists, revealing critical information about the investigation. With his wife Audrey distressed over the escalating risks and his colleagues unaware of his covert activities, Felt battles growing isolation and moral dilemmas. Turning into an anonymous informant known as "Deep Throat," his actions set in motion a series of events that challenge not only his integrity but also the ethical standing of powerful political figures.