This article is a recap of Black Mirror’s season four episode “Crocodile.” It contains spoilers and discussion regarding the episode's plot.

There are no crocodiles in “Crocodile,” the third episode of Black Mirror’s fourth season. In fact, it’s set in Iceland, where there are no crocodiles to be found at all.

But as in many of the series’ nightmarish episodes, “Crocodile” takes place in a near future in which we’ve finally figured out how to tap into, record, and even manipulate our memories. Crocodile cognition isn’t my particular specialty, but digging around a bit, I discovered that crocodile brains are apparently almost entirely limbic, which means they comprise the systems that house memories and the functions that support those memories, like smell and emotion.

That tracks with the episode, which returns to a favorite Black Mirror subject: the ways our lives would be changed if our memories were suddenly available outside our own heads. The episode is written by series creator Charlie Brooker, and though Black Mirror always feels like a latter-day Twilight Zone, this is one of the more Twilight Zone-y episodes I’ve seen, especially in its ending, which is both a twist and a punch to the gut.

But most of “Crocodile” plays out like a slow-motion nightmare, where you can see the next beat coming just before it happens, and then have to sit and watch in horror as it does. It’s a good match for director John Hillcoat, who in addition to the post-apocalyptic Cormac McCarthy adaptation The Road also made The Proposition, a brutal Western and the only one I’ve ever really loved. Hillcoat is good at stark brutality that packs an emotional wallop — and “Crocodile” has that brutality in spades.

In “Crocodile,” an accidental death leads to a chain of intentional ones

The episode starts out with Mia (Andrea Riseborough) and her boyfriend (Andrew Gower) dancing in a club and taking some kind of drug, then cuts to them driving through the pristine Icelandic landscape, sharing a joint and singing. Suddenly, a body hits the windshield, cracking it. They’ve hit a man on a bike, and they stop, stunned.

The man’s dead, and Mia’s boyfriend — terrified that he’ll be sent to jail for manslaughter — convinces her to help him put the body in a sleeping bag, weigh it down with rocks, and drop the corpse along with the bike into the water.

Then we fast forward about 15 years. Mia is now a star architect “not just of buildings, but of communities,” a man says, introducing her at a conference. (It appears to be in Reykjavik.) She has a son and a husband and a chic haircut and a lovely home. After giving a talk at the conference, she gets a knock on her hotel room door. It’s her ex-boyfriend, the one with whom she shares the dark secret, and they haven’t seen each other in a few years.

It turns out the ex-boyfriend got sober almost 10 months earlier, and in pursuit of making his amends with those he’s hurt, he’s going to write a letter to the family of the man they accidentally killed.

Mia panics. She has a family. She has a career. He promises to keep her out of it, but she says “they” can trace her anyhow — and exactly what she means by that soon becomes clear. He’s inexorable, though, so Mia makes a snap decision: She shoves him to the floor and chokes him until he dies. (The sound his neck, or maybe his windpipe, makes when it snaps is among the more disturbing sounds I’ve ever heard.)

Mia can barely believe what she’s done, but she moves quickly, shoving the body under the bed, ordering room service so as to have a cart at her disposal, and flicking on a pay-per-view porn film, reasoning that the record of the in-room transaction will provide cover for her if she needs an alibi.

At the same time, though, a man outside on the street is hit by what appears to be a self-driving pizza-vending truck. (This is the most utopian bit of the episode.) He’s okay — it’s just his arm that’s broken — but seeing a man hit by a vehicle rattles Mia, who pulls down the shades and watches from between the slats. Using the room service cart, she brings her ex-boyfriend’s body down to the garage, gets in the car, and disposes of him. The next day, she checks out of the hotel (paying for the porno on the way out) and goes home to her family.

Intercut with Mia’s story is another one: a woman (Kiran Sonia Sawar) works for an insurance company, investigating claims. In this near-future reality, she carries around not just a notebook but a tiny, non-invasive device that can pick up people’s short-term memories and display them on the screen of an oscilloscope-like device.

The investigator’s job is to determine what the claimants are owed based on what happened. She helps uncover the claimant’s memories, not just by asking them to remember, but by triggering two powerful memory aids: the senses of smell and hearing. It’s not a perfect solution, especially since, as she says, memories are unreliable, emotional, and sometimes even malleable.

The man hit by the pizza truck is a claimant, and viewing his memories sets the inspector on a series of additional interviews of those who may have witnessed the accident, which could help determine how much fault the pizza truck company bears and how much the claimant should receive.

At this point in the episode, it’s pretty clear that the inspector is going to end up knocking on Mia’s door. The episode seeds small details about the memory device along the way — in particular, the fact that a year earlier the government had begun requiring citizens to submit to the memory scans. If they don’t, the inspectors have to report them.

“Crocodile” sees how our memories, made public, could wreak havoc

And this is where the true nightmarish scenario of “Crocodile” kicks in. It’s not just about your memories being readable with a fancy device. That’s a bit terrifying, of course — I’d venture to say that nobody wants that. This isn’t totally new territory for Black Mirror, which covered similar ground in episodes like season one’s “The Entire History of You”, but “Crocodile” takes it in a new direction.

The inspector insists to everyone she scans that their memories are confidential, unless it’s shown that they’re hurting themselves or other people, which seems to put some people at ease. My immediate reaction to that is a raised eyebrow, but the more I think about it the more I realize it’s just a natural extension of something we already do: give big tech companies the ability to hang onto our personal information — our emails, our text messages, our pictures — via “the cloud,” where all data seems to reside in 2017. Certainly, Google and Apple and AT&T promise they won’t use our data for evil. But they also sell it to advertisers. And we just give it away.

It’s not a huge leap from there to government-mandated memory reading, and what’s even more frightening is the admission that memories are not just unreliable, but suggestible. The inspector is able to change the color of a woman’s jacket in someone’s memory just by telling him it was a different color. What’s to keep a sinister agent from implanting or changing memories that are then used in a court of law?

That’s the nightmare scenario, but it’s not what “Crocodile” is interested in exploring. Instead, the episode becomes something like the origin of a serial killer: Mia is forced to go to increasing lengths to hide her dark secret. By the end of the episode, she’s killed three adults and is even forced into doing the unthinkable: murdering a child. (Unfortunately for Mia, it’s not just humans that have tappable memories — guinea pigs do, too.)

Black Mirror episodes usually try to use a dystopian technological scenario to say something true about humans; “Crocodile” muses that there may be a reason humans’ memories aren’t accessible to others — that there’s something fundamental to our humanity, and to the smooth running of our societies, about being able to have private memories shaped by our emotions and sensations. This is well-trodden ground for science-fiction, and for that reason “Crocodile” doesn’t feel all that innovative. It’s certainly not one of the more memorable (ha) episodes of the show.

But it’s haunting, and as I watched I was reminded of other films I’ve watched recently that dealt with the malleability and emotional impact of memories. One is Don Hertzfeldt’s animated short films World of Tomorrow and World of Tomorrow Episode 2: The Burden of Other People’s Thoughts, in which the memories of a character become places for deep sadness, and also a kind of resource from which its future clones can mine emotions. The other is this year’s film Marjorie Prime, a haunting meditation on how memories and love are bound up together, and how they can morph and change over time.

Musings on the changeability and emotional heft of memory may not be what “Crocodile” intended for me to walk away with; it’s an often-graphic episode about the potential for violence inside us that could be unlocked if our memories threatened our lives. But its title points to a part of the brain that is governed by memory, emotion, and sensation, and as Mia’s emotions war with her rational brain, her plight isn’t hard to sympathize with — and I wonder how much of it is plausibly in our future.