Jake J. Gittes (Jack Nicholson)’s Timeline and Summary

Jake agrees to help a woman who claims to be Evelyn Mulwray to find out if her husband, Hollis, chief engineer of the water department, is having an affair.
Jake trails Hollis and discovers that someone is stealing water from the city of L.A. He also snaps pictures of Hollis kissing a woman (not his wife).
The pictures wind up in the paper, and Hollis turns up dead.
When Jake realizes the woman who claimed to be Evelyn was an impostor meant to set Hollis up, he suspects murder.
Jake investigates the water theft and questions the real Evelyn, along with the deputy chief of the water department, Russ Yelburton, and later Evelyn's father, Noah Cross.
Eventually, he discovers that someone is stealing the water, buying up land under the names of retirement home residents and dead people and moving the water there.
He grows more attracted to Evelyn and sleeps with her.
But Jake finds that Evelyn seems to be holding captive the woman her husband was kissing. After he realizes Hollis was drowned in the pool in Evelyn's backyard, Jake confronts her.
It turns out that the mystery woman is actually Evelyn's own sister/daughter—the child born of incest with her father, Noah.
Noah, Evelyn reveals, murdered Hollis.
Jake tries to help Evelyn escape and confronts Noah about the murder.
But, in the end—in Chinatown—the cops shoot Evelyn dead after she tries to kill Noah. Noah pulls his daughter/granddaughter away from the scene, leaving Jake behind with his sadness and confusion.