Working as a uniformed patrolman, Frank Serpico (Al Pacino) excels at every assignment. He moves on to plainclothes assignments, where he slowly discovers a hidden world of corruption and graft among his own colleagues. After witnessing cops commit violence, take payoffs, and other forms of police corruption, Serpico decides to expose what he has seen, but is harassed and threatened by his peers. His struggle leads to infighting within the police force, problems in his personal relationships, and his life being threatened.