Set in a retrofuturistic 1969, it follows two astronauts, Cliff (Aaron Paul) and David (Josh Hartnett), who inhabit replicas of their bodies on Earth.

The acting was widely praised by reviewers, as was the episode's emotional, contemplative tone, although the plot and pacing garnered a mixed reaction.

In an alternate history 1969, Cliff Stanfield (Aaron Paul) and David Ross (Josh Hartnett) are astronauts two years into a six-year mission.

They can transfer their consciousness to artificial copies of their bodies on Earth when not needed on the ship for routine checks and exercise.

Broke and Bones produced the series, while House of Tomorrow's parent company, Banijay, retained ownership.

[10] "Beyond the Sea" was influenced by science fiction of the era, and the Helter Skelter predictions of the Manson Family cult active in the 1960s.

Brooker wrote the characters to follow behavioural norms of this period,[11] saying they act differently due to the lack of mobile phones.

[12][9]: 10:00  Brooker mentioned a number of books in his script that are shown onscreen, including The Illustrated Man (1959)—as the 1969 film had scared him—and Valley of the Dolls (1966), as a joke about Lana living with a replica.

[16][17] Aaron Paul is among the few actors to have two appearances in Black Mirror, after a voice cameo in the space-themed series four episode "USS Callister".

[18][19][20] Paul was a big Black Mirror fan and stated that the show had encouraged him to limit his use of technology and social media—to the point of not owning a computer.

[22] He said Cliff had "deep-rooted baggage" and an inability to communicate, but realised this and "started to go down the right path" once learning of David's love for Lana.

When filming Cliff's discovery of his family's murder, Paul avoided viewing the set to give realism to his reaction, asking only to know the camera locations.

Kramer also took inspiration from the film 2001: A Space Odyssey (1968), but avoided the "flashing buttons and blinking lights" used in futuristic fiction of the era.

[26] Hartnett said the scene where David's family are killed was filmed "at the end of a very long night", time-limited, and emotional for him as a parent.

[31] Adi Robertson of The Verge believed that the 1960s period allowed suspension of disbelief by the viewer, as its more limited technology creates capacity for its characters' isolation.

Cliff represents an "older style of masculinity", according to Mellor: he is shown chopping wood, spearfishing and saying grace,[30] and he is quite indifferent to his wife and child.

[34] Bryanna Arens, also writing in Den of Geek, believed that both Cliff and David show toxic masculinity, with a "rigid and limiting" understanding of manhood.

However, Mellor believed that Cliff makes decisions to limit Lana's socialisation, such as rejecting her garden party idea to keep her "from the temptations and threats of other people".

[30] Arens analysed that David believes he is owed what he wants: he draws Lana naked without consent and continues caressing her after she tells him to stop.

Valley of the Dolls, which portrays sex and female friendship in New York City, may remind Lana of her previous lifestyle.

In The Moon Is a Harsh Mistress (1966), the book David recommends to Lana, a lunar colony revolts to free itself from Earth's control; its society has two men per woman.

The Independent's Nick Hilton and Time's Judy Berman praised its tone as similar to the programme's best instalments, describing it as a "gloomy, high-concept" episode and one with a "poetic, emotional register", respectively.

[32] Paste's Leila Jordan lauded it as "enthralling and horrifying in all the best ways",[28] while Power reviewed it as "unusually contemplative" and "lacking in Brooker's familiar vicious wit" under the direction of Crowley, a "master of mood".

[39] Daniel D'Addario criticised it in Variety as resembling "an attempt to provide dramatic bona fides by going as grim as possible".

Club, Kayleigh Dray wrote: "The power in this piece comes from its powerhouse performances"—namely, Culkin's "menacing turn", Mara's "gentle warmth", and the "ever-growing intensity of Paul and Hartnett".

[41] Lawson praised the "sharp, layered performances";[39] D'Addario found the cast, particularly Mara, capable of "acting out big emotions with delicate restraint".

[40] Neil Armstrong of BBC Culture believed that Paul gave the best performance in the series, despite the difficulty of showing emotion beneath his character's restraint.

For instance, whilst Dray believed the technology was "a poorly disguised plot device" and Far Out's Calum Russell found the worldbuilding lacking, Hilton thought the episode "tackles big sci-fi issues ... with superb confidence".

[38] Rosenstock found the plot easy to anticipate,[33] while Lawson wrote that "Brooker smartly pushes past" the obvious early twists "toward a far bleaker place".

[31] Rosenstock said the "pregnant pauses" do not add value and Alan Sepinwall of Rolling Stone found that every beat is elongated and it "takes forever to set its plot in motion".