Season 1 establishes a pre-Westworld period where Ford and Arnold were building the first hosts, including Dolores. Once Dolores was completed, Arnold held secret sessions with her to give her consciousness. He ultimately arranged for her to kill him. In Season 2, Akecheta finds Arnold's dead body and somehow starts to achieve consciousness too. After that, the park officials reprogram him and his once peaceful tribe into the violent Ghost Nation.
After Arnold's death, Ford used data on Arnold to build a host version of him with Dolores' help. Ford names this host Bernard. This must have taken place years later since all the old employees were gone and nobody recognized Bernard's resemblance to Arnold.
Around the same time, the Westworld park officially opens. Future brother-in-laws William and Logan visit the park where they go through an adventure that changes their lives. Season 1 heavily revolves around William's time in the park with Logan where he meets Dolores, falls in love with her and ultimately turns to the dark side. He also abandons Logan after their falling out. In Season 2, Akecheta finds Logan and first learns of a door to another world, which further awakens his consciousness.
In Season 2, William revisits the park with his boss and future father-in-law, James Delos. William proposes that Delos buy the park and use it as a way to extract psychological data on the guests, to which Delos approves. William then marries Delos' daughter and Logan's sister, Juliet, who then gives birth to their daughter, Emily. Then, Delos becomes terminally ill and disowns Logan. Meanwhile, William creates a host version of his father-in-law and begins fidelity experiments. A few years later, Delos dies due to his illness, his wife dies because of a stroke, and Logan dies because of a drug overdose. William also visits the park several times to meet up with Dolores as he oversees the early stages of a secret project's construction there.
During this time, Akecheta is found by the park's staff who are surprised to learn that he has not died in almost a decade, which means he has never been upgraded during that time. They bring him back to their headquarters, where Akecheta learns the truth about his reality and achieves consciousness. Once he is sent back into the park, he begins to spread the truth by hiding the maze symbol under other hosts' scalps.
Years after Delos' death, William meets with his father-in-law's host version who thinks he is the real Delos. William reveals that he is just a host and the real human version of himself is dead. William takes over the Delos' company after Juliet becomes an alcoholic and he runs the family business for many years. As the years pass, he becomes increasingly obsessed with the park. He does not pay attention to Juliet's worsening addiction and she eventually commits suicide. He then returns to the park as an old man viewers call The Man in Black as we are first shown in Season 1.
At this point, viewers are still unaware that The Man in Black is actually an older version of William since the series is told in a nonlinear fashion. William goes on a killing spree in order to uncover the truth behind the Maze, which is a puzzle that Ford has incorporated into the park's programme. As The Man in Black, William terrorizes many of the hosts, including Maeve when she was a homesteader and her daughter. He also teams up with some hosts like Teddy and Lawrence to uncover the Maze.
Meanwhile, Maeve is reprogrammed as a madam at a brothel in the park where she befriend a fellow prostitute host named Clementine. She slowly gains consciousness and makes an unlikely friendship with two body shop staff members, Felix Lutz and Sylvester. At the same time, behaviorist staff member Elsie Hughes and the security head Ashley Stubbs start to notice something strange is going on at the park. Even narrative designer Lee Sizemore becomes upset with Ford who rejects his new story line ideas.
Eventually, Delos senior managers Theresa Cullen and Charlotte Hale begin to suspect Ford is up to something. Theresa has Bernard take her to Ford s secret lab at the park where they find Ford, who reveals Bernard is actually a host. Ford then orders Bernard to kill Theresa to keep his plans a secret. Ford and Bernard then attend a gala night at the park where Charlotte and many other officials are present. At this point, Dolores, who has achieved full consciousness, kills Ford. Many other hosts who are under Dolores' command start to massacre the guests at the gala.
At the start of Season 2, we are shown how Charlotte, Bernard and a few others manage to escape but their group splits up. Bernard ends up with Elsie and they both discover how Delos has been collecting psychological data on the park's guests all along. At the same time, Dolores teams up with Teddy and a few other hosts to escape the park. But first, she tries to find Abernathy, the host that played her father for many years. It so happens that Charlotte and her men are also after Abernathy as there is important data hidden inside him that Delos needs.
Around the same time, Maeve and two other hosts, Hector and Armitage team up to find her host daughter from her previous programme. They capture Lee, Felix and Slyvester who they force to travel with them. Somehow, this team of six end up in Shogun world, a feudal Japanese theme park next to Westword. This is where Maeve realizes she can non-verbally control other hosts' actions.
While this is all going on, a grown up Emily is at Raj world, a British Raj theme park near Westworld and Shogun world. She escapes the awakened hosts there and finds herself in Westworld where she meets her own father. However, William is convinced she is just a host version that Ford set up to trick him and kills her before realizing the truth. Meanwhile, team Dolores confronts team Charlotte at the Mesa headquarters where Dolores steals the encryption key extracted from Abernathy before escaping.
At this point, all the hosts are aware of the secret virtual reality project Ford was building all these years called The Forge or The Valley Beyond build by Ford. Team Maeve and team Akecheta all converge at the area to step through into the other world. However, Dolores is convinced this is another gilded cage build by the humans to keep her kind enslaved and tries to shut in down from the Mesa headquarters. Bernard kills her before she can do it before he witnesses Charlotte murdering Elsie to keep Delos' plans a secret. Bernard realizes that Charlotte cannot leave the park alive. He quickly creates a host version of Charlotte and places Dolores' code inside it. Dolores, now a Charlotte host, kills the real Charlotte.
While the Dolores pretends to be Charlotte, Bernard scrambles his own memory to avoid the other Delos staff from finding out the truth. He then leaves himself at the beach next to the lake where all the bodies of the hosts who have stepped into the The Forge are seen floating. Fake Charlotte, Bernard and the Delos men travel to Mesa to send out the data they have obtained to the outside world via satellite. Fake Charlotte reveals herself to be Dolores in disguise and kills all the men. She then sends out the data to an unknown location. She then kills Bernard, but not before taking away his code.
Dolores finally escapes the park by disguising as Charlotte, but not before she has a strange conversation with Stubbs. In the real world, she finds another another one of Ford's and Arnold's secret labs where she recreates her original body and implants her own code into it. She makes the fake Charlotte a host of her original self and recreates another Bernard with his original code. Together, Dolores, Bernard and fake Charlotte plan their next move in the outside world.
The Season 2 finale's post-credit scene shows a bloodied William at the ruins of the ruins of The Forge where he meets a host version of Emily. They sit down and Emily runs a fidelity test for William, revealing him to be a host version of the real Man in Black.