An undertaker, Amerigo Bonasera, watches a judge suspend the sentences of two men who savagely beat his daughter. Furious, he decides to seek true justice from Don Vito Corleone. In a Los Angeles hotel, celebrity Johnny Fontane drunkenly strikes his second wife, actress Margot Ashton, for cheating on him, but he cannot bring himself to hit her beautiful face. His voice and career failing, Johnny takes his problems to his Godfather, Don Corleone. Meanwhile, Nazorine, a New York baker, wants to prevent his employee, Enzo, from being deported back to Italy. The Baker knows that only Don Corleone can help.
It is August 1945. The Godfather, Don Vito Corleone, the Sicilian-American boss of the Corleone Family, one of the Mafia’s Five Families that dominate organized crime in New York City, is hosting the wedding of his daughter, Connie Corleone, at his lavish Long Beach home. Also attending the wedding are Don Vito’s sons. The hot-tempered Sonny Corleone sneaks off to have sex with his mistress, Lucy Mancini. Fredo Corleone, the middle son, dutifully mixes with the wedding guests. Don Vito’s youngest son, the World War II hero Michael Corleone, sits with his non-Italian girlfriend, Kay Adams. The Don has amassed great wealth and power through his control of criminal rackets such as gambling and extortion. He is therefore a “man of respect” to whom people come seeking extralegal justice and other services in exchange for pledging their everlasting loyalty to their Godfather. The Don meets with Bonasera, Fontane, and Nazorine. He agrees to solve their problems but chastises Bonasera for his foolish faith in the legal system.
Later that evening, Don Corleone visits his dying Consigliere, Genco Abbandando, in the hospital. When Genco passes away, the Don appoints as new Consigliere his adopted son and lawyer, Tom Hagen. Don Corleone sends Hagen to convince Hollywood film producer, Jack Woltz, to cast Fontane in his new picture. Woltz refuses because Fontane stole his trophy girlfriend. In retaliation, The Don’s henchmen sever the head from Woltz’s prized racehorse and place it in his bed. A horrified Woltz gives Fontane the part. The Don also sends his caporegime, Peter Clemenza and his soldiers to beat the two men who assaulted Bonasera’s daughter. Don Corleone’s political contacts, whom he keeps on his payroll, then prevent the deportation of Nazorine’s helper, Enzo.
After Connie’s wedding, Don Corleone meets with Virgil “The Turk” Sollozzo, a heroin dealer allied with the Tatagglia Family who offers a large profit incentive if the Corleone Family will use its political connections to protect his drug distribution ring. The Don declines to get involved because he believes drugs to be a dirty business that would scare away his political allies. The Don is suspicious of Sollozzo, so he sends his enforcer, Luca Brasi to spy on The Turk, but Sollozzo and Bruno Tatagglia (the son of the leader of the Tatagglia family) garrote Brasi in a nightclub. At Christmastime, Michael and Kay are on a date in New York City when Michael sees a newspaper headline proclaiming that his father has been shot. Spurned by Don Corleone’s refusal to join his drug operation, Sollozzo pays off the Don’s bodyguard, Paulie Gatto, to betray his boss. Sollozzo then sends assassins to hit the Don, but they fail to kill him. Afterwards, Sollozzo kidnaps Tom Hagen and demands that he ensure that Sonny, the now acting Don, makes a deal with Sollozzo over drug distribution.
Sollozzo then attempts to kill Don Corleone in his hospital room with the help of Mark McCluskey, a police captain on Sollozzo’s payroll. Michael foils this second assassination attempt by bringing more guards for his father. Clemenza and his soldier, Rocco Lampone, kill the traitor, Paulie Gatto, in his car. Michael then develops a plan with Sonny, Hagen, and the caporegimes, Clemenza and Sal Tessio to murder Sollozzo and McCluskey to prevent more attempts on Don Corleone’s life. Michael meets with Sollozzo and McCluskey in a restaurant, where he retrieves a pistol stashed in the bathroom and shoots the other two men. Michael then flees to Sicily to evade murder charges.
Johnny Fontane is attempting to sleep with a young actress, Sharon Moore, but she rebuffs his advances. A dispirited Johnny then reconnects with his ex-wife, Virginia, and their two daughters before Tom Hagen offers Johnny a film production deal backed by Don Corleone. Johnny agrees to the deal to please his Godfather and invites his former musical partner, Nino Valenti, to join him in the venture. Jonny and Nino record music and produce several films, but Nino grows disenchanted with the debauchery of Hollywood life and descends into alcoholism.
A flashback follows Vito Corleone’s rise in New York’s criminal underworld. Born Vito Andolini in the town of Corleone, Sicily, the adolescent Vito flees to America after the local Sicilian Mafia boss murders his father and brother. In America, he changes his last name to “Corleone” and works in the Abbandando family’s grocery store in Little Italy. Vito eventually collaborates with a young Tessio and Clemenza to highjack merchandise from delivery trucks and resell it at a profit. When Don Fanucci, the neighborhood Black Hand, gets word of Vito’s activities, he threatens violence if Vito and his partners don’t give him a cut of the profits. Rather than pay Fanucci, Vito murders him, establishing himself as a “man of respect” whose fearsome reputation proceeds him. Vito performs favors for people who profess their loyalty to him, and he raises a family with his wife, Mama Corleone. He becomes rich bootlegging alcohol during Prohibition, then forms an olive oil importing company and uses his crew of soldiers to force competitors out of business. Vito operates his legitimate businesses as fronts for his growing crime empire. He helps to organize the other Mafia organizations into Five Families that control specific territories, thereby assuring peace in the underworld and his own position as the most powerful Mafia Don in New York.
The novel returns to where it left off in 1947. Kay Adams is working as a teacher in her native New Hampshire. Michael has been gone for two years, and she must fend off questions from police detectives who are investigating his connection to the murders of Sollozzo and McCluskey. Back in New York, Carlo Rizzi constantly beats his wife, Connie Corleone because he thought the Corleone’s would make him rich and all they gave him was a lowly bookmaking job. Carlo’s abuse of Connie invokes Sonny’s rage, and one day Sonny beats him mercilessly in the street. Knowing that Sonny will not kill his sister’s husband, Carlo refuses to fight back. Meanwhile, the Corleone Family is at war with the Five Families over the murders of Sollozzo and McCluskey. As Don Corleone returns home from the hospital, the Family adds extra security to his large estate, known as the mall. Fredo moves to Las Vegas to work the Family’s casino business while Sonny, Hagen, Clemenza, and Tessio “go to the mattresses” and continue to battle the rival Families.
The novel flashes forward. The undertaker Bonasera is having dinner at home when Tom Hagen calls on him to perform his service for Don Corleone. Bonasera goes to his funeral parlor, where Don Corleone arrives with the bullet-ridden corpse of Sonny. The Don asks Bonasera to make his son’s body presentable for an open-casket funeral. The novel then shifts back to the present, where Sonny’s bloody fight against the Five Families has left many casualties but has not ended the war. Tom Hagen disapproves of Sonny’s tactics but cannot interfere because Sonny is the acting boss while Don Corleone recovers from his injuries. One evening, Connie answers a call from one of Carlo’s mistresses. She confronts him and he angrily beats her again. She then calls Sonny to ask for a ride to the mall. Sonny becomes enraged and drives to Connie’s apartment by taking the Jones Beach Causeway. When he stops at the tollbooth, the car in front of him blocks him in, and the toll taker pulls out a gun and shoots him. Two gunmen emerge from the blocking car and shoot him again. When Sonny’s bodyguards arrive at the scene, they call Tom Hagen, who calls Carlo to tell him that he and Connie will move to the mall, where Carlo will have a more prominent position in the Corleone Family. Later that evening, Hagen informs Don Corleone that his eldest son is dead. The Don forbids any acts of vengeance.
Don Corleone organizes a peace meeting with the head of the Five Families, as well as the heads of Families from across the country. At the meeting, Don Corleone advises the other bosses to come to a reasonable agreement in order to stop the war and spare more bloodshed. He insists that drug trafficking will destroy the Mafia because it will chase away their political allies who view it as a dangerous and illicit business. He reminds the other Dons that most of their children work in legitimate society as pezzonanavnte (big shots), and that moving away from criminal enterprises is a less violent and destructive path to take in the future. Don Emilio Barzini and Don Phillip Tattaglia, however, demand that Don Corleone must share his political connections to give protection for the other Families who want to deal in drugs because the business is too profitable to ignore. Don Corleone reluctantly agrees to do so on condition that the other Families promise they will not retaliate against Michael for the Sollozzo and McClusky murders. The other Dons agree, and Don Corleone adjourns the meeting.
The Don returns to the mall and tells Hagen that he plans to semi-retire, and that the Consigliere should prioritize bringing Michael home safely from Sicily. Don Corleone now knows that Barzini was allied with Sollozzo and Tattaglia all along, and that he must ultimately be dealt with if the Corleone Family is to retain its power.
Meanwhile, Lucy Mancini has been living in Las Vegas for a year since Sonny’s death. There, she meets Dr. Jules Segal, the handsome physician at the Corleone Family’s casino hotel. They begin dating, and Segal learns that Lucy has a condition that interferes with her sex life. He tells her that a Los Angeles surgeon he knows can fix her up with a simple surgery, and Segal’s concern makes her fall in love with him. He then reveals that he performs abortions on showgirls, many of whom Fredo Corleone impregnates. A few weeks later, Dr. Frederick Kellner operates successfully on Lucy. After her surgery, Lucy greets Johnny Fontane and Nino Valenti. Segal hears Fontane’s raspy voice and convinces the stubborn singer to let him examine his throat. Segal finds warts on Johnny’s vocal chords and suggests a surgeon who can remove them. He also warns that Nino’s alcoholism will soon kill him. A month after Lucy’s operation, she and Segal are engaged to be married.
The novel goes backwards in time. Michael Corleone has been hiding in the town of Corleone, Sicily. He is staying at a villa owned by the local Mafia boss, Don Tommasino and Tommasino’s uncle, Dr. Taza, both of whom are friends of Don Corleone. Michael spends his days learning to read Italian and walking amidst the beautiful Sicilian landscape with his shepherd bodyguards Calo and Fabrizzio. One day, while hiking the fields, Michael comes across a beautiful peasant girl named Apollonia and immediately desires her. He goes to her village, where he convinces Apollonia’s father, Signor Vitelli, to let him marry his daughter. The wedding, however, alerts Michael’s mob enemies to his whereabouts, and a car bomb meant for Michael kills Apollonia instead. Now that his enemies believe him to be dead, Michael returns to America. He reunites with Kay and the two marry. Michael, however, now plans to succeed his father as Don of the Corleone Family, and he warns Kay that she will not be his partner in life and cannot ever ask about his Family business.
Michael decides to close all of the Corleone Family’s eastern business operations and move to Las Vegas to invest fully in casinos. In Vegas, he meets Fredo, Lucy, Fontane, Nino, Segal, and casino magnate Moe Greene. He gives Segal a job in a new hotel and makes Greene “an offer he can’t refuse” to buy Green’s share of the casino. Green, however, does refuse. Meanwhile, Fontane’s new films are a big success, but Nino ultimately drinks himself to death. Michael returns to New York and plots a master plan with Don Corleone to settle all Family business by murdering the Corleones’ enemies. Michael also tells Clemenza and Tessio that they can form their own New York Families after the move to Las Vegas, but that they must stay loyal to the Corleones until then.
Don Corleone dies one morning in his garden. After the Don’s funeral, Michael sets his master plan into motion. His men kill Moe Greene, Don Barzini, and Phillip Tatagglia. Michael then has Tessio murdered, who he had figured out was plotting against him with Barzini. Finally, Michael has Clemenza garrote Carlo in a car for betraying Sonny to Barzini’s hitmen. W his Mafia rivals dead, Michael now formally succeeds his father as Don and restores the Corleones’ status as New York’s most powerful Mafia Family. Kay threatens to leave him when she learns that he had Carlo killed, but Hagen convinces her that the murder was in the Family’s best interest. She converts to Catholicism and moves to Nevada with Michael and their two children. Before the move, however, Kay spends her remaining days in New York praying in church for her husband’s eternal soul.