In August 1945, during the lavish wedding reception of his daughter Connie, Don Vito Corleone, head of a large New York crime family and "godfather" to the Italian-American community, listens to requests for favors, honoring a long-standing Sicilian tradition that a father cannot refuse a request on his daughter's wedding day. While FBI agents jot down license plate numbers of the guests, and hundreds of celebrants dance, eat and gossip in the Corleone family's Long Beach compound, Don Vito, assisted by his foster son and consigliere , Tom Hagen, listens to a plea by the undertaker Bonasera, who seeks justice for two American boys who mercilessly beat his daughter. After mildly chastising Bonasera for refusing his friendship in the past, Don Vito agrees to help in exchange for some future service. Next, Don Vito greets the amiable baker Nazorine, who seeks help in preventing the deportation of Enzo, a young apprentice baker who wants to marry Nazorine's daughter. Outside, as the family welcomes guests such as crime boss Don Emilio Barzini and Don Vito's godson, popular singer Johnny Fontane, Michael Corleone arrives at his sister's wedding with his American girl friend, Kay Adams. Michael, college educated and a decorated soldier during World War II, relates stories about Luca Brasi, a large, violent man who is unquestioningly loyal to Don Vito, but tells her "It's my family, Kay, not me." In Don Vito's study, the final supplicant is Johnny, who cries that powerful studio head Jack Woltz refuses to give him an important part in a new war movie, even though it would be a perfect, career-saving role for him. After slapping Johnny like a child and admonishing him to be a man instead of a "Hollywood finocchio," Don Vito comforts him and promises to help. Just before his father-daughter dance with Connie, Don Vito talks with his son Santino, nicknamed Sonny, and Tom, telling them that Connie's new husband, Carlo Rizzi, may have a job, but should never be privy to the family's business. Don Vito also instructs Tom to fly to Los Angeles to speak with Woltz. At Woltz's studio, when Tom politely suggests that Johnny be cast in the war film, Woltz angrily dismisses him with curses and ethnic slurs. However, after Woltz has learned that Tom is representing the Corleone family, he invites Tom to his lavish estate and apologizes for his earlier rudeness. When the men sit down to dinner after Woltz has shown Tom his beloved race horse, Khartoum, Tom again asks for the part to be given to Johnny, prompting Woltz to erupt in a rage, shouting that Johnny "ruined" a young starlet with whom Woltz had been having an affair, thus making him appear ridiculous. One morning a short time later, Woltz discovers the severed, bloody head of Khartoum in his bed, prompting him to scream in terror. Back in New York, Don Vito is approached by Sollozzo “The Turk,” a ruthless, Sicilian-born gangster who owns poppy fields in Turkey. Sollozzo, who has the backing of the rival Tattaglia family, proposes that the Corleones finance his drug operations. Although Tom and Sonny have argued that narcotics are the way of the future, and Sonny tries to say so in the meeting, Don Vito refuses to risk losing his political influence by embracing the drug traffic and declines Sollozzo's offer. Later, Don Vito privately asks Luca to let it be known to the Tattaglias that Luca might be interested in leaving the Corleones. Just before Christmas, when Luca meets with Sollozzo and one of the Tattaglias, he is caught off guard, stabbed through the hand and strangled. That same evening, Fredo, Don Vito's meek, oldest son, tells him that their driver, Paulie Gatto, has called in sick. Before entering his car, Don Vito decides to buy some fruit from a vendor and is shot several times by assailants who flee before Fredo can react. Tom is kidnapped by Sollozzo that night, and later, as Michael and Kay leave the Radio City Music Hall, Kay notices a newspaper headline announcing that Don Vito has been killed. Stunned, Michael immediately calls Sonny, who relates that their father is barely alive in the hospital and insists that Michael return to the safety of the family’s Long Beach compound. Late that night, Tom is released by Sollozzo, who is infuriated that Don Vito has survived the attack, and warns Tom that he and Sonny must make the narcotics deal with him and the Tattaglias. At the compound, Sonny and Tom try to insulate Michael from their discussions about the family business, knowing that Don Vito had wanted him to have a different kind of life. While arguing over whether or not to take Sollozzo's deal, they receive a package of a dead fish, a Sicilian symbol that Luca "sleeps with the fishes." Now the hot-headed Sonny insists that there will be a war between the Corleones and the Tattaglias. Sonny tells Clemenza, one of his father's lieutenants, to buy mattresses and other supplies to house their men in a safe place during the war and instructs Clemenza to kill Paulie for his part in Don Vito's ambush. A few days later, frustrated by his enforced idleness, Michael goes into New York City to have dinner with Kay. After telling her that she should go home to New Hampshire, but not saying when they will see each other again, Michael goes to visit his father. When he finds the hospital floor deserted and Don Vito's room unguarded, Michael checks to make certain that his father is alive, then calls Sonny to relate what has happened. After moving Don Vito's bed with the help of a nurse, Michael whispers in his ear, "Pop, I'm with you now." Moments later, when the baker Enzo innocently arrives to pay his respects, Michael advises him to leave because there will be trouble, but Enzo enthusiastically offers to help. Michael and Enzo then wait on the steps of the hospital. Because of their menacing appearance, when a car stops, the thugs inside see what they think are Don Vito's guards and drive off. Just then, several police cars appear, and the abusive Capt. McCluskey starts yelling at Michael for interfering, then brutally punches him in the face before Sonny, Tom and their men arrive. The next day, Sonny argues that they must hit back at Sollozzo, even though the corrupt McCluskey is his protector. Because Sollozzo is now asking for a meeting with Michael, who is regarded as a "civilian," Michael volunteers to kill both Sollozzo and McCluskey. A bemused Sonny does not want Michael involved, and Tom argues that this is business, not personal, but Michael insists that to him it is business. When Sonny learns from a police informant that the meeting will be held at Louis, an Italian restaurant in the Bronx, Clemenza arranges for a gun to be planted in the men's room, then teaches Michael how to kill at close range. At the restaurant, Sollozzo offers a truce to Michael if the family agrees to his terms. After excusing himself to go to the men's room, Michael retrieves the gun from behind the toilet, walks to the table and shoots both McCluskey and Sollozzo in the head, then coolly walks out to a waiting car. To avoid being the victim of a revenge killing by the Tattaglias, Michael is forced to leave for Sicily for an extended period without saying goodbye to Kay. When Don Vito, who is now recuperating at home, hears that Michael killed Sollozzo and McCluskey, he weeps over Michael's involvement. While Michael is in Sicily, a wave of violence envelopes the Corleones, the Tattaglias and the other members of the five New York crime families. At the same time, Michael falls in love at first sight with a beautiful Sicilian girl, Apollonia, and soon marries her. Some time later, when a pregnant Connie hysterically calls home and tells Sonny that Carlo has beaten her, Sonny, who had previously warned Carlo never again to hit his sister, impulsively races away from the compound without waiting for his bodyguards. When he stops to pay a toll on the deserted highway, he is ambushed by several henchmen who riddle his body with bullets before speeding away. That night, after Tom reveals Sonny’s death to his father, Don Vito says that the killing must now end and orders no more acts of vengeance. Later, he accompanies his son’s body to Bonasera’s, where he tearfully asks the undertaker to repay his debt by making Sonny presentable to his mother. Shortly thereafter, Don Tommasino, Michael’s protector in Sicily, tells him of Sonny’s death and says that he and Apollonia must leave for their own safety. As they are about to leave, Apollonia decides to surprise Michael by driving his car. Moments after Michael sees one of his bodyguards, Fabrizio, suspiciously run away, Apollonia dies when the car explodes. In New York, Don Vito has called a meeting of representatives of the five crime families of New York and New Jersey, asking for peace. After arguments on both sides, the families reach a peace accord and agree to enter the narcotics trade. As they are driving home from the meeting, Don Vito tells Tom he finally realized at the meeting that Barzini has always been behind the Tattaglias and was responsible for everything. Some time later, Michael goes to New Hampshire, where Kay has been teaching. Although he has been home for more than a year and not contacted her, he tells her that he loves her and asks her to marry him. She is reluctant, and does not understand why Michael now works for his father, but agrees because of her feelings for him and because he assures her that within five years, the Corleone family business will be completely legitimate. Soon Michael becomes the tacit head of the family as Don Vito semi-retires. Michael plans to sell the family’s olive oil business, which had been a legitimate cover for their gambling and prostitution operations, and become the sole owner of a Las Vegas casino. He sends Carlo to Las Vegas, as well as Tom, privately telling the disappointed Tom that there will be trouble at home and Tom is not a “wartime consigliere .” Weeks later, on a business trip to Las Vegas, Michael is annoyed that Fredo, who was sent to Las Vegas several years before, has let himself become subservient to Moe Greene, their partner in the casino. When Greene angrily refuses to sell his interest in the casino, Fredo sides with Greene, prompting Michael to warn him never again to side with someone outside the family. One afternoon, Don Vito warns Michael about Barzini and predicts that the person who suggests a meeting with Barzini will be a traitor setting Michael up to be killed. That same afternoon, while Don Vito plays with Anthony, Michael and Kay’s three-year-old son, he has a fatal heart attack in his vegetable garden. At Don Vito’s funeral, Salvatore Tessio, another Corleone family lieutenant, tells Michael that Barzini would like a meeting. Tom is surprised that Sal, rather than Clemenza, is the traitor, but Michael realizes that, for an ambitious man like Sal, it is the smart move. He then reveals that the meeting will be held after the baptism of Carlo and Connie’s baby, also named Michael, for whom he has agreed to be godfather. While the baptismal ceremony takes place, Barzini, Tattaglia and several other Corleone enemies are gunned down in New York and Greene is killed in Las Vegas. At the compound, Tom confronts Sal, who says to tell Michael that it was only business, and resigns himself to his fate. That afternoon, Michael confronts Carlo, promising him leniency if he will just confess that he set Sonny up to be murdered. Though terrified, Carlo believes Michael and reveals that Barzini was behind it. Moments later, thinking that he will be driven to the airport, Carlo enters a car and is strangled from behind by Clemenza. When the Corleones are packing to move to Las Vegas, an hysterical Connie rushes into Don Vito’s old study and accuses Michael of murdering Carlo. Kay tries to calm her down, but when she and Michael are alone, she asks if it is true. Michael initially erupts in anger, then says that, just this one time, Kay may ask him about his business, then answers “No,” and the couple embraces. This satisfies Kay until she sees Clemenza kiss Michael’s ring and address him as “Don Corleone,” before his lieutenant, Neri, closes the study door.