"Trace Decay" begins with Dr. Ford and Bernard debriefing after the murder of Theresa, as the shattered, furious host demands to know why his creator made him do this. The good doctor replies with a quote from Frankenstein about the insignificance of one life in the grander scheme of things; it's a weird reference to make, since Frankenstein is a story about an inventor who creates a humanoid monster only to have it turn against him and destroy all he holds dear, but I guess if you're going to own yourself, you might as well do it through fine literature.
Ford tasks Bernard with covering up the murder, promising that in return he'll remove all memories of Bernard's relationship with Theresa and his part in her death, so that he can wake up as fresh and untroubled as Dolores once did on her pillow every morning.
That's always been the promise of Westworld: actions without consequences. Far more than adventure, it offers the questionable balm of moral indifference. It's a place where everything that happens is designed to be meaningless, where you don't have to care. It's an appealing idea because, when things matter, it means that you can get hurt, and people will do just about anything to not experience pain.
Bernard certainly feels that way, so he plants Theresa's body in the park in a way that implicates her as a traitor and blames her for the malfunctioning hosts, paving the way for Ford to resume work on his precious narrative. Ford then makes good on his promise: "As exquisite as this array of emotions is," he says, "even more sublime is the ability to turn it off." It's an even more complicated moment when you learn that Bernard himself was the programmer behind the more nuanced emotions of the hosts, a robot who created his own feelings only to see them erased.
As Bernard turns toward a fugue state, all his fellow hosts finally seem to be coming out of it. Even stolid, dependable Teddy finally has an erratic memory of his own: the Man in Black dragging Dolores out to the barn in a previous loop. Teddy ties up his traveling partner, but finds he still can't shoot him despite the urging of a pretty blonde woman whom he rescued from one of Wyatt's massacres — and who very quickly stabs him in the shoulder and reveals that she's working with Wyatt. It's time for Teddy to "come back to the fold."
Charlotte Hale isn't quite ready to call it quits, so she digs up the human-masturbation hand motion that is Lee Sizemore and gives him a new assignment: helping her finish what Theresa started. Turns out Theresa wasn't stealing from Delos so much as she was stealing for Delos, and now that she's had her little "slip-and-fall" accident, the board needs another way to snag Ford's proprietary code. Plan B is use a blank host as a walking USB stick, but they need Sizemore to give it a skeletal backstory in order to navigate it out of the park. They couldn't have picked a better vessel: the former Peter Abernathy, a.k.a. the malfunctioning host we last saw whispering, "These violent delights have violent ends."
Meanwhile, Dolores finally finds her way "home" with William, only to find out that the place she's been looking for is now just a dusty strip of desert with a burned-out church in the background. Her flashback shows us a town that used to be there, the same town where the hosts were originally trained and refined before the park opened. Somehow, it all ended in a massacre that looks very much like the one we've seen Teddy talking about, though he remembers soldiers dying while Dolores sees it as a slaughter of townspeople — two stories that seem to overlap and converge, like slightly different versions of the same myth. At first it seems like a man is shooting, but in the end, Dolores sees the gun in her own hand, and then points it at her head.
William pulls her away, telling her, "This place isn't good for you. You're trapped in memories, bad ones." Dolores's flashbacks seem very much like a symptom of PTSD, where the unresolved traumatic events of the past feel like they're happening over and over again in the present. Indeed, a lot of the hosts' function (or malfunction) can be seen through the lens of trauma. The way they are forced to "forget" their agonies echoes the disassociation that trauma survivors often experience when the pain of a moment or a memory becomes too much to bear; in extreme situations, this disassociation can even fragment their sense of self in fundamental ways.
The reason that the hosts are coming apart at the seams — or, arguably, finally coming together — is because they are not allowed to heal from their trauma. Healing would require them to remember, to suffer, to allow themselves to finally turn toward the pain rather than away from it.
For that, we can look to Maeve, the host who committed the original sin of not forgetting. Through a campfire story by the Man in Black, we learn that she marked both the beginning of his heel turn and the beginning of this robot revolution. After the suicide of his wife in the real world, the Man in Black decided to return to Westworld and see exactly what kind of person he was by doing what so many video-game players have done: randomly killing a bunch of innocent characters just to see how it feels. He picked Maeve, a random homesteader, and casually murdered her and her daughter for no good reason — and felt nothing.
Maeve, on the other hand, felt everything, and became hysterically upset and unresponsive to Bernard's voice commands after Westworld techs dragged her back to the labs. Ford calms her with a carefully chosen piece of music and prepares to wipe her memory. "You need not suffer, Maeve," he says soothingly. "I'll take it from you." Unlike Bernard, she doesn't want to forget. "Please, this pain is all I have of her," she begs. Ford erases her memory anyway, a cruelty that he no doubt sees as a kindness. But Maeve is stubborn as always, and instead of fading away gently, she stands up and stabs herself in the neck.
In the present, she has not only come to terms with the past but decided to take the first meaningful steps toward a real future. She wants to escape from Westworld once and for all. Despite Sylvester's best attempts to "brick" her, she convinces Felix to make some fundamental changes to her code. The first thing she does upon waking is cut Sylvester's throat for being such a bastard, and then she announces, "It's time to recruit my army."
When Maeve returns to Sweetwater, she finds that she can not only write her own story, but everyone else's. She walks through the world like a omnipotent third-person narrator, scripting the story that men like Ford and Sizemore once scripted for her. Eventually, she causes enough ruckus that Delos takes notice of her behavioral problems and sends a team to retrieve her. Although she's by herself when the men in suits burst through the door, I'm far more afraid for them than I am for her — especially since I suspect that her robot army may already have recruits.