HBO’s puzzle box sci-fi series Westworld is returning for its fourth season on June 26. Here’s everything you need to remember before watching: 

Season 1

Westworld is a theme park owned by a company called Delos and populated by incredibly lifelike robots, or hosts, which allow guests to role-play a western adventure — and treat the hosts, who constantly have their memories wiped, as cruelly as they please. It’s one of a number of parks that Delos owns, including Shōgunworld and Warworld. 

The hosts were designed by Dr. Robert Ford (Anthony Hopkins) and Dr. Arnold Weber. But Arnold, who wanted to create consciousness in the hosts, decides he must prevent Westworld from opening, so he engineers a massacre of the hosts that also results in his own death. The park still opens, but years later, Ford updates the hosts so they can subconsciously retain memories, allowing some to gain consciousness.

Upon achieving sentience, one of the hosts, Dolores Abernathy (Evan Rachel Wood), murders Ford and various Delos board members in a massacre at the park. Another host, Maeve (Thandiwe Newton), becomes aware she’s a host and that she had a daughter in a past storyline. She plans to leave the park, only to turn around to go back and find her child. 

Other characters in the first season include Bernard Lowe, a Delos programmer played by Jeffrey Wright, who’s revealed to be a host modeled after Arnold Weber. Meanwhile, in the past, we follow William (Jimmi Simpson), a Delos executive who falls in love with Dolores. But after her memory is wiped and she no longer remembers him, William goes off the deep end, growing increasingly cruel and turning into the “Man in Black,” played by Ed Harris in the present. 

Season 2

The second season picks up with a now-sentient Dolores leading a violent robot uprising in the park. She’s joined by Teddy (James Marsden), her love interest who becomes disillusioned with her war on humanity and, after realizing Dolores has changed his code to make him do terrible things, commits suicide. 

Maeve, who now has the ability to control hosts, makes her way back into the park and finds her daughter, but she now has another host mother. Speaking of daughters, William’s daughter confronts him in the park, and he murders her thinking she’s a host imposter — only to find out it really was her. 

It’s eventually revealed Delos has been trying to figure out a way to transfer human consciousness into hosts in an attempt to achieve immortality. We also learn Delos has been gathering a massive amount of data on guests, effectively copying their consciousness, which is stored in The Forge. But The Forge also houses a virtual world known as the Sublime, where the hosts can live peacefully without humans. 

The Westworld hosts ultimately make their way inside the Sublime, including Maeve’s daughter and Teddy. But Maeve stays behind, apparently dying in a final battle, while Dolores heads off the island. 

Season 3

Now set on the mainland, the third season introduces a company called Incite, which operates an advanced AI called Rehoboam that predicts future events. It was created by a man named Engerraund Serac (Vincent Cassel), who hopes to use the machine to steer the world toward a path in which humanity doesn’t destroy itself, charting a course that everyone must follow. But there are those known as “outliers” who don’t fit into this future Rehoboam has projected, so Incite captures them and keeps them at a hidden facility. Some outliers are freed after being subjected to intense reconditioning, and Serac’s goal is to reprogram the outliers like robots. To do so, he needs the trove of biometric data gathered on the guests at Westworld, so he buys Delos to obtain it. 

This pits him against Dolores, who has several hosts working for her that are actually just copies of herself, including Delos executive Charlotte Hale (Tessa Thompson). The real Charlotte was killed at the end of season two, but the Dolores host version is given control of Delos, and she unsuccessfully tries to prevent Serac’s buyout. The fake Charlotte begins to form a bond with the real Charlotte’s family, who end up getting killed by Serac. 

Dolores also recruits Caleb Nichols (Aaron Paul), a veteran and “outlier” who was reconditioned and tasked with capturing other outliers for Incite. A resurrected Maeve is on Serac’s side for most of the season, but only because he promises to reunite her with her daughter, and the key to the Sublime is supposedly inside Dolores. William, meanwhile, is grappling with guilt after his daughter’s death and is institutionalized by the fake Charlotte, but he makes it out with a new goal: save the world by killing all the hosts. 

Dolores obtains Incite’s files on everyone on Earth and makes them public, meaning the entire world now knows what lies in their future and how they’re going to die — leading to rioting and global unrest. We spend most of the season believing Dolores is trying to violently overthrow the human race, but it’s revealed her goal was really to save humanity by destroying Rehoboam to build a new, freer world. Caleb gains control of Rehoboam and shuts it down, and Maeve stabs Serac, joining Caleb’s side. But Dolores apparently dies after Serac erases her memories. 

Bernard, who began season three in hiding because the massacre at Westworld was pinned on him, ends the season by putting on a VR headset to go inside the Sublime — which it turns out he had the key to, not Dolores — to find “an answer to what comes after the end of the world,” concluding the apocalypse can’t be prevented and Rehoboam was just putting it off. We then see Bernard taking off the headset sitting on the same motel bed covered in dust, apparently many years later. Meanwhile, William travels to a Delos building to destroy the hosts, and he confronts fake Charlotte, who now has her own sinister agenda separate from Dolores that involves creating more hosts. Charlotte brings out a new host version of William, who slices the real William’s throat, seemingly killing him. 

And that brings us to season four, in which the real Dolores is apparently dead and Evan Rachel Wood is playing a mysterious new character named Christina. If it’s anything like past seasons, viewers can expect to spend plenty of time questioning the nature of their reality in the weeks ahead.