Nick visits Gatsby for breakfast the next morning. Gatsby tells Nick that Daisy never came outside the previous night, but rejects Nick's advice to forget Daisy and leave Long Island. He tells Nick about the early days of his relationship with Daisy. He remembers how taken he was by her wealth, her enormous house, and even by the fact that other men had loved her. To be with her he let her believe he was of the same class as her. One night they slept together, and he felt he had married her. Then he left for World War I. Daisy waited for a while and then drifted away from him and into marriage with Tom Buchanan.
Gatsby's story explains his actions. He was in love with the idea of Daisy: Daisy's love gave Gatsby an identity as a young man, and made his manufactured "new money" identity legitimate. To preserve that identity, he had to have her. Note that "old money" types like Tom could avoid the war while poor nobodies like Gatsby couldn't.
Gatsby and Nick finish breakfast. As they walk together, the gardener tells Gatsby he's going to drain the pool. But Gatsby tells him to wait. He says he hasn't used it once all summer, and would like to. On his way out, Nick tells Gatsby that he's worth more than all of the "rotten crowd… put together." Gatsby smiles broadly.
Nick always disapproved of the way Gatsby lived his life, but he respected the purity of Gatsby's dream. He certainly preferred it to the "rotten crowd" that used Gatsby.
At work that day, Nick falls asleep. The phone wakes him: it's Jordan. Their conversation quickly turns unpleasant and one of them hangs up on the other. Nick finds that he doesn't care.
The events of last night have convinced Nick to cut ties with the old money world of Tom and Daisy.
Next, Nick relates what happened at Wilson's garage after Myrtle's death. Wilson spent all night talking to Michaelis about Myrtle, revealing that she had a lover and his suspicion that the man driving the car must have been her lover because she ran out to meet it. He told Michaelis how he had confronted her and told her she was sinning in the eyes of God. It was near dawn at this point, and Wilson was staring into the eyes of T. J. Eckleburg when he mentioned God. Wilson says he has a way of finding out who was driving the car and later that morning disappeared from the garage.
Myrtle's death destroys Wilson's dream, leaving him nothing. The Roaring Twenties conflict between old and new money has destroyed him: he can't even distinguish an advertisement from God. Wilson's "way" of finding out who killed Myrtle is mysterious. Fitzgerald is building tension.
At two, Gatsby went for a swim, leaving word that he was to be alerted if any phone call came. None came. Later that afternoon, Nick and some of Wolfsheim's men working at Gatsby's house discover Gatsby, shot dead in his pool. Wilson's dead body is close by lying in the grass.
The recklessness of the Roaring Twenties destroys every relationship: Myrtle and Wilson, Myrtle and Tom, Daisy and Gatsby, Jordan and Nick. Only "old money" prevails: Daisy returns to Tom.