Spoilers for season 4 of "Westworld" ahead.

In the fourth episode of season 4 of "Westworld," the various story threads finally came together into a cohesive narrative, and last week's fifth episode, "Zhuangzi," dealt with the fallout of that collision of character arcs, following a number of hosts in Hale's (Tessa Thompson) "perfect world" as they begin to realize that their lives are not all they seem.

Christina (Evan Rachel Wood) went on a date with Teddy (James Marsden) that forced her to question the nature of her reality, while Hale, William (Ed Harris), and Clementine (Angela Sarafyan) handle a bizarre phenomenon they call "outliers," who are infecting the hosts with suicidal ideation. The episode stays in the city, however, so the only humans shown are the outlier extraction team working with Caleb's (Aaron Paul) daughter C (Aurora Perrineau), who barely manage to escape. In this week's episode, "Fidelity," we'll get to see what's going on with Bernard (Jeffrey Wright) and C, who found Maeve's (Thandiwe Newton) robo-corpse out in the desert, and maybe get some more details on what's happening with host Caleb, too.

The episode title, "Fidelity," refers to the concept of fidelity when information is copied. A copy of a copy of a copy is going to have less fidelity than the original, as small details are lost in the re-creation. Fidelity is accuracy to a source, in this case, determining how accurate a host is to its programming or human "source." Hale has been testing the host versions of Caleb for fidelity, trying to get one as close to the original as possible so she can discover some secret he's kept. The humans must check one another to ensure no one has become a host, which is another kind of fidelity. If last week's episode was about the characters questioning their surroundings, this week is about them questioning their very selves. Much like the first few episodes, this one jumps back and forth between two main narratives, so I'll focus on them one at a time in the name of clarity. It's almost like an "A" and "B" plot in a sitcom, just with murder robots!

Repairing Maeve

The episode starts with a flashback, because "Westworld" loves a flashback, and young Frankie and her mother Uwade (Nozipho McLean) are helping people escape during Hale's parasitic takeover. Everyone freezes so that the creepy white robots can inspect them, and unfortunately the escapee, J (Daniel Wu), blinks when a fly lands on his eyelashes, alerting the robot sentries. They manage to escape and go to an old abandoned house to hide for a bit. Uwade introduces J to the others and Frankie shows him her radio and tells him about her messages to her father. J tells her that he'll never be her brother and that her father is dead and she's wasting her time. Since we know she's still looking for him as an adult, it's an especially bitter statement, and the series knows it, cutting directly to present-day Frankie, who goes by C as an adult. She's with Bernard, and they have Maeve's body in the backseat.

They head back to the park, which is now completely taken back by the desert and fallen into ruin. Bernard needs supplies to fix Maeve, however, and knows there will be plenty in an abandoned park designed to keep a whole stable of hosts in working order. C begins to question Bernard because he knows so much about hosts and he tries to deflect, explaining, "This park shares an architect with Westworld. I used to work there." That's pretty rich, given that Bernard is a version of Westworld's original architect, Arnold, but he did also technically used to work for Delos, so he's not lying. C asks him what he did at the park and she explains that he programmed the hosts. When she accuses him of allowing the "puppets" to get out of hand, he deflects again: "Delos was known for keeping its employees in the dark as much as the guests."

Bernard begins to rebuild Maeve with C's help, and the whole thing is reminiscent of "Frankenstein," including a bath in a milky substance for Maeve and a transfer of "brains," because Maeve's marble-like brain pearl is too damaged by the desert to work properly, so they transfer it to that of another host. While they work, Bernard explains how the park worked and how Hale used it to gain information on all of humanity, first by tracking data through the hats and then by recording them and watching them through one-way mirrors. "To control the world, she needed to understand," he tells C. Unfortunately, their chat is interrupted by C's comrades, back from their mission in the city.

Who Are You, Really?

Bernard hides Maeve's mid-transfer pearl inside of an old piano and blows off the dust, then goes back to patching her up. C notices the tender care that Bernard gives to Maeve and comments on it, explaining that her mother got sick and required the same kind of care. "She's not an ordinary host, is she? You knew her," she asks, then tells Bernard that the last time she saw Maeve, she was with her father and he never came back. She says that hosts don't understand pain because "feelings are just an affect to them, a switch you can turn on or off." Her worldview is shaped by her experiences, but it's the exact same kind of binary thinking that led to this whole mess in the first place. Bernard, himself a host with big feelings, brushes her off with another mystical comment about the situation making strange bedfellows of them all.

J and the rest of the team enter the room and J grumbles about a mole. C, not trusting Bernard, shoots him. He doesn't drop dead, which reveals he's a host, and C is furious. She and Bernard are left alone for a moment and he warns her that there is a mole, but it's not him. She leaves him to fiddle with Maeve and finds J, who tells her the exact same thing about there potentially being another mole. C goes out "on patrol" and runs into her girlfriend (Morningstar Angeline), who wants to know what's going on. C's not trusting anyone at this point, so she takes her girlfriend captive and locks her in a room away from everything. "You think I'm one of them?" she asks, and C can only answer "maybe." This season has taken a lot of inspiration from films like "Invasion of the Body Snatchers," but this week it's going full "The Thing," complete with paranoia about personal identity! C apologizes to her girlfriend before heading out, telling her that if she's not "one of them," she's safer away from things anyway.

C starts talking with J, who listens as she tells him about leaving messages to her father. She still leaves them, apparently, on their old frequency. J is nicer in his reply than he ever normally would be, alerting C to the fact that he's been replaced by a host. He was caught while in the city and switched, and is in fact the mole. The two begin to fight, and things aren't looking good for C.

Caleb's Existential Horror Hell

While C and Bernard deal with a doppelganger and bringing an old friend back from the dead, the latest host version of Caleb is going through his own existential nightmare. He's still with Hale, who's grilling him about the outliers. Apparently she believes they all started with Caleb, because he was able to resist her all of those years ago.

"Once you told me that you could fight off the effects of the parasite because you have something I don't have."

He refuses to tell her what that thing is, and she's furious. She offers him an incentive: a quick and painless death. Apparently the host bodies she's made for her Caleb tests only last for a few days at most before they start breaking down, sort of like the replicants in "Blade Runner" but at a significantly quicker rate. He's still defiant, telling her that maybe she'll have better luck with the next guy. He taunts her, telling her that he knows Frankie/C is alive and that Hale can't catch her. Hale reveals that she sent a "visitor" to C, an insider to take care of things, then leaves. Caleb bangs on the glass door and realizes his hand is breaking from the action, then he turns and sees another Caleb host, badly deteriorating. He's rotting and has clawed bits of his face away, and he tells less-rotten Caleb that "dying is just the beginning." He taps on the glass toward a sand-timer Hale had turned marking Caleb's remaining days; Caleb opens the top to discover a small cylinder that pricks his finger and causes him to fall unconscious.

A Whole Crop Of Calebs

Caleb goes through some more flashbacks, revisiting how he met his wife when she was a nurse and he survived the first robo-attack with Maeve, but is pulled back to reality when one of the faceless sentry robots terminates his unit and the whole room begins to fill with flames. He appeared dead enough for the robot to believe, but now he has to escape the flames or be dead for real. He manages to get out through a vent in the floor when he finds an arrow carved in it, presumably by one of his past selves. He pops back to the flashback and asks his wife if he is "now" and she teases him about asking such an existential question. He realizes it's just a memory and pops back to the present, where he's knocked himself unconscious after falling into a pit beneath the cell full of scorched, dead Calebs. He gets up and sees a handprint of soot on the wall similar in size and shape to his own hands and follows it, trailing handprints to a supply closet. One of the sentry robots finds him but he manages to kill it.

Meanwhile, Clementine and Hale have a little chat about the escapee Caleb. Hale complains about how humans ruin everything and starts interrogating Clementine, asking her if she ever lets the humans in the city get under her skin. Clem is careful in her words, telling Hale that she never gets close to the outliers and "prefers the sheep."

Escapee Caleb is indeed still on the loose, crawling through the vents. He finds another past version of himself that looks dead but is actually just sort of decomposing and alive. The only way out of the vents is a long fall, and the dying Caleb tells the escapee to "use" him. Escapee Caleb does, in fact, use the other Caleb, crawling on top of him and using the other's body to break his fall. He's a human-host airbag, basically. Ow. From there he manages to make it up on the roof of the building, where he records a message for Frankie and sends it out through the satellite, calling her "Cookie" (is that where "C" comes from?) and then Frankie:

"You're going to win. You're going to do what I couldn't, because you are strong, so much stronger than me. This world, this world she made, it's a lie. It's not real. But what you have, what you have is real. I'm sorry that I failed, that I haven't been there for you, and now it has to be you. But you can do this. You're my warrior. I love you."

This Caleb is starting to decompose, and the skin on his face is starting to loosen, but he's managed to do the one thing he's always wanted: apologize to Frankie for leaving.

It All Comes Together

Out in the desert, C hears Caleb's message over the radio frequency in her all-terrain vehicle. The host version of J shoots the radio, but she heard it and that's all that matters. She shoots him a bunch of times and he continues to walk toward her, T-1000 from "Terminator 2"-style, but she's not afraid. He asks her where Maeve's pearl is so he can destroy it and she tells him that she took it and stashed it, directly behind him. He turns to find Maeve alive and looking well, and she drives a knife into his face. Welcome back, queen. She and C talk about Caleb and where to go from here, and Maeve tells her it's time to finish what she and Caleb started all of those years ago and finally stop Hale.

Back in the city, Hale finds the Caleb who escaped and tells him of her disappointment in him. She was letting him escape so she could give him a bit of hope, maybe inspire him to do what none of the other Calebs could. Instead, she feels like he "wasted it all on a worthless apology." She tells him that there's no way C heard it and he tells her that it doesn't matter, because Hale will still lose. Humans didn't infect the hosts. He then delivers the sickest burn in series history, telling her that the hosts would rather die than live in her world:

"They're not infected, they're just trying to get away from you."

She kills him and has all of the current model Calebs destroyed. The clues, like the arrow on the grate, are removed, and she builds another, brand new Caleb: Caleb number 279. The final moment is Hale sitting down in the fidelity test room and saying the magic phrase: "Caleb. Wake up."

This week's "Westworld" was still fairly straightforward, though some of the Caleb flashbacks seemed like fake-outs to try and get people guessing at more mysteries. All of this is building toward a fight between Maeve and Hale, however, and I cannot wait to see it.

New episodes of "Westworld" debut Sundays on HBO and HBO Max.

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