Black Mirror has left us reeling with many a twisted ending over the years, but Season 6 wields one of the most chilling to date.

In the episode "Beyond the Sea", Black Mirror recurring player Aaron Paul and Josh Hartnett star as astronauts Cliff and David, who each have "Earth replicas" that stay with their respective families. These robot doppelgängers work with connected pods, so the pair can enjoy their life back home while completing a six-year mission in space together.

But everything goes to shit. It's an understatement that begs an explainer, so let's torture ourselves one more time and dig into the unsettling, bleak, and deeply horrible ending of "Beyond the Sea."

What leads to "Beyond the Sea"'s tragic ending?

One fateful night, David's life is obliterated as he's forced to watch his family murdered in front of him (well, his replica) by anti-replica cultists, claiming "to restore the natural order." The 1969 Manson Family comparison is semi-subtle. Cast as David's wife, Auden Thornton slightly resembles the late Sharon Tate. And the Chitty Chitty Bang Bang cinema outing places this episode in 1968, one year before the notorious Manson Family murders.

Credit: Nick Wall/Netflix

After this despicable triple homicide, the cultists destroy David's replica, leaving him without a connection back to Earth or any means to grieve his family outside the space station. And all this sees an irreversible change in David.

SEE ALSO: How does Aaron Paul tie the 'Black Mirror' universe together?

Out of profound kindness, Cliff's wife Lana (Kate Mara) suggests her husband lend his replica to his mourning co-worker. The link to their home planet might help with his grieving, offering him a chance to get out of the station and "breathe some air."

This session on Earth affects David so deeply that he craves more, inventing an oil painting project to justify continued visits. But he becomes infatuated with Lana, getting closer to her, and attempting to convince her to let him stay in Cliff's place. Lana lambasts David for this bold proposal. Then, her son Henry, lashes out by vandalizing David's oil painting, spurring the latter to smack the boy. Lana doesn't tell her husband about David's advances. But she uses this parenting overreach as a plea to Cliff: David should not return. However, Cliff shrugs off her request.

Credit: Nick Wall/Netflix

Eventually, Cliff finds out about David's obsession with his wife through the sexy sketches on the station. "It's pure fantasy, I got mixed up," David claims when confronted. Cliff finally has a frank conversation with Lana about what she wants and how she feels, and back in the station, Cliff declares his "ownership" over Lana, firmly cutting off access to David.

The widowed astronaut internalizes his agony over this loss, for now.

What happens at the end of "Beyond the Sea"?

David essentially takes from Cliff what was taken from him: his family and his connection to Earth.

"You have got it all and you don't even care," David tells Cliff.

Fabricating an incident outside the space station, David urges Cliff into a spacewalk, then highjacks his replica. Returning to the station, Cliff realizes David has used his link, quickly runs to plug it in, and wakes up in his Earth house, with his hands and face covered in blood.

"What did you do?" Credit: Nick Wall/Netflix

Black Mirror uses inference to devastating effect in this scene, as we don't actually see what David has done to Cliff's family. But from the smeared blood down the staircase through to the pool of blood in the kitchen, it's clear this has been a terrible struggle. Ultimately, Cliff finds what he fears the most — Lana and his son Henry murdered by his own (replica's) hand.

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Aaron Paul's performance in this scene is nothing short of shattering.

We follow Cliff through his bloodied house witnessing his reaction intensify as he gets closer to the horrible truth. Thanks to exceptionally compelling performances from Harnettt, Mara, and Paul throughout the episode, the loss is much deeper for the viewer than that of David's family at the beginning (although it's deeply disturbing), as we didn't really get to know their connection with each other.

Credit: Nick Wall/Netflix

Essentially, David attempts to take back what was stolen from him, but from Cliff — his wife, his son, and his beautiful home. When that fails, he takes them away. And he frames Cliff for the crime.

It's a brutal form of punishment, horribly disciplining Cliff for not appreciating having everything David lost.

What's even more chilling is the final scene: David awaiting Cliff's reaction on his return, pushing out a chair in unspoken, but certain acknowledgment.

David knows Cliff can't return to Earth — he'll be put in jail for his family's murder, as no one but Cliff and Lana knew about David's visits. Plus, Cliff has previously mentioned the spacecraft is a two-person job to operate. So, he's stuck in space for the next four years with his family's murderer. If he kills him in revenge, Cliff has no way back home.

It's pure, dark, cold hell. And there's nothing either of them can do about it but kill each other or continue work as usual.

How to watch: Season 6 of Black Mirror is now streaming on Netflix.