Ex-convict Elrod Davis looks up fellow ex-con Gary Baker to become the ""driver"" in a bank robbery. Serpico joins the hold-up team and convinces Baker, who is married, to drop out. Before Baker leaves he betrays Serpico.
After several unsuccessful attempts to close down Tiller's numbers racket, Serpico and Atkins suspect a leak within the task force. Chief suspect is Serpico's childhood friend and gubernatorial candidate Assistant District Attorney Bobby Delaney.
Several attempts to break a drug ring headed by ""The Indian"" fail. Serpico intentionally tips off ""The Indian's"" go-between Grace to an upcoming raid. He gets suspended but gains ""The Indian's"" trust. Serpico wants to meet and personally bust ""The Indian."" Serpico reunites drug courier Heather with her father, and he has romantic interest in the hospital doctor caring for Heather.
Serpico must protect John Maloney, a presidential candidate for the truck drivers union, from an assassination ordered by Jack Powell, the current leader. Maloney's daughter Rita falls for Serpico. Vern Ross, Maloney's right-hand man, has a crush on Rita and secretly works for Powell.
Jenny, one of Serpico's ex-girlfriends, helps two men steal furs in the garment district. With Jenny's help, Serpico passes himself off as a fur designer. A sting operation fails and Serpico realizes he told Jenny about it. He confronts her and Jenny reveals that she was blackmailed. When Jenny double-crosses the robbers and her life is in jeopardy.
Vince Cipolla, a 20-year veteran on the police force, is dying of leukemia and wants to leave money for hia wife. He gives confidential information on the locations of gambling and prostitution houses to two criminals who share their ill-gotten gains with Cipolla. Serpico follows the clues to Cipolla, who once instructed him, and tries to help.
Sullivan assigns Serpico to gain the confidence of a sadistic loan shark, Alex Demico. Marion Wagner, an undercover officer, plays the dangerous role as Demico's woman.
Serpico is on the trail on arms broker Raoul Christie who is illegally selling M-16s to criminals. Serpico gets caught in a department turf war when he gets Christie's man Lincoln killed; Lincoln was an informant. Serpico befriends Christie's favorite prostitute, Erica Molinas.
Serpico, posing as an explosives expert, tries to learn the plans of a group of revolutionaries. Kirko suspects Serpico is a cop. Lucy, the sister of Jerry the leader, falls for Serpico.
Serpico gathers evidence against Nagel who owns a cargo shipping business that smuggles Serbians into the United States for a price. Serpico tries to help an illegal immigrant Serbian brother and sister, who know about the smuggling operation, from being deported.
Atkins assigns Serpico to work with Duffy a veteran detective who's part of a task force trying to bust Eddie Pickett, a drug dealer and ex-cop. Serpico doesn't like Duffy because he's reckless and a ""showboat.""
Magda is a Soviet gymnast who wants to defect. After nearly being kidnapped by a serial killer she finds sanctuary in a synagogue where Rabbi Shotness promises to help. Magda explains that her parents, who are in the Soviet Union, will be in Vienna in two days where they will seek political asylum. Magda doesn't want news of her defection made public until her parents are safe. However, Serpico desperately wants Magda because she can identify the serial killer who kidnaps women, rapes them then kills them with an ice pick to the heart. Meanwhile the Soviet secret police is also looking for Magda.
Serpico looks for the killer who targets women campaigning for mayoral candidate Gene Rincon. After Serpico discovers that a shady real estate businessman has contributed money to Rincon's campaign, he suspects that Rincon himself is involved with the murders.
Marcus, a young adult, watches a gang throw a woman off the roof. Serpico and other officers search for Marcus in order to protect him from the gang. Marcus's school teacher, Michelle, knows where he is and Serpico tries to convince her to tell him.
Serpico is assigned to protect state witness Viveca who is scheduled to testify before a grand jury in three days. Sullivan assigns Carol Hinterman to assist Serpico who has his doubts about her abilities. Mobster Vitorio La Bella is desperate is kill Viveca at any cost.