SPOILER ALERT: Do not read if you have not watched the “Arkangel” episode of the fourth season of “Black Mirror,” which first premiered on Netflix Dec. 29.

The most unsettling thing about “Black Mirror” is often how the characters, living in a not-so-distant world from our own, are completely dependent upon invasive technology that more often than not ends up ruining their lives. No episode may exemplify this more than the fourth season’s “Arkangel.” It features a young mother (Rosemarie DeWitt) implanting a chip in her daughter’s head to not only be able to track her physical movements via GPS and any health changes via a biometrics system — but also control what she experiences by scrambling images that might be offensive or harmful, and tap into her daughter’s POV to see what she sees at any given moment.

“It felt the most immediate to me of all of them so far,” DeWitt tells Variety about the episode. “I feel like you could do a version of it now. I don’t have teenagers, but I feel like you could probably track them and do all sorts of things.”

The episode – or movie, as DeWitt and director Jodie Foster call it (and indeed, last season’s installment “San Junipero” won the Emmy for TV movie) — starts with DeWitt’s character giving birth, and immediately becoming frantic over her child’s health, since she doesn’t immediately cry. Those fears deepen as her daughter gets older, especially when she wanders away for a few minutes on a playground. That incident inspires putting the chip in the child, setting the mother down a dark road of control.

“It was easy for me to justify the reasons behind it and the love behind it, and that’s where she goes off-line a little bit, and also how her reactiveness gets the best of her,” DeWitt says. “With the single parent model, you experience betrayal differently. You experience lying from your kids differently. And something gets ignited in her because this is her only person in the world, so fair or unfair, she reacts from that place.”

As the episode continues, she does momentarily turn off the filters to allow her daughter to live her life more fully. But when typical teenage rebellion rears its head, it sends her spiraling back to her old habits.

“There’s an interesting change where there’s a moment where she realizes her daughter’s lying to her, and she lies back, and there’s the first moment of unsaidness between the two of them that’s this fissure,” Foster explains. “So she changes. She goes dark and becomes somebody who’s now fighting a battle to win control.”

“Arkangel” does not explore violent or otherwise age-inappropriate elements assaulting the child on a daily basis as a way to explain why the filters needed to be turned on in the first place. “I didn’t think it was necessary, and I thought it could actually distract from what the meaning was,” Foster says of staying away from graphic imagery.

Instead, what was important to Foster was focusing on the mother-daughter dynamic to show how “in a weird way, they’re also the same person.” This allowed the episode to feel intimate — “like a Bergman movie,” she says — as a character study.

And as the young girl grew up and her mother removed her filters, a shift was made to showcase her experimentation. “The important thing for her was to know she was free to make choices and have experiences,” Foster points out.

The one exception when it came to graphic content was the violence the daughter inflicted on her mother in a moment of uncontrolled rage after learning just how far her mother went to control her.

Both DeWitt and Foster point to this as the most “devastating” element of the episode, not for the act itself but because of how the two ruined their once-symbiotic relationship.

“It’s the self-fulfilling prophecy. She started saying, ‘Please don’t leave me. Is she okay? Where is she?’ And she engendered the exact result that she most feared,” Foster says of DeWitt’s character. “By insisting she control her daughter so she wouldn’t leave her, and handicapping her daughter so she wouldn’t leave her, and taking over control of her body so she wouldn’t leave her, she exacted what she feared the most. And now she will be alone.”

Season 4 of “Black Mirror” is streaming now on Netflix.