The episode follows Robert Daly (Jesse Plemons), a reclusive but gifted programmer and co-founder of a popular massively multiplayer online game who is bitter over the lack of recognition of his position from his coworkers.

He takes out his frustrations by simulating a Star Trek–like space adventure within the game, using his co-workers' DNA to create sentient digital clones of them.

Aboard the spaceship USS Callister, Captain Robert Daly (Jesse Plemons) and his crew destroy their arch enemy Valdack's (Billy Magnussen) ship, but he escapes.

New programmer Nanette Cole (Cristin Milioti) praises Daly's work on Infinity, but the more assertive Walton interrupts to show her around the office.

When Daly returns home, he opens a development build of Infinity which is modded to resemble his favourite television show Space Fleet.

They use those photos to blackmail the real-life Nanette into ordering a pizza to Daly's apartment and stealing the DNA samples while he answers the door.

The firewall detects Daly's modded build and locks his controls, rendering him physically unable to exit the game as it is deleted around him.

"[3] As a big fan of Star Trek, Bridges suggested many elements from it that are incorporated in the episode, as well as borrowed concepts from the film Galaxy Quest, which involved normal people suddenly pulled into an inescapable science fiction setting.

[10] Brooker tells Den of Geek that the episode is not intended as an attack on Star Trek, a show that was "wildly ahead of its time".

Director Toby Haynes notes that "they always wanted Jesse Plemons for the role of Daly", and that the filming dates and other cast were based around him.

[12] Milioti accepted the role having only seen a few pages of the script; she said in an interview that Nanette is "a woman in charge [fighting] against a small-minded, misogynist bully".

[20] He then came up with the idea that the best voice would be Paul's character Jesse Pinkman from Breaking Bad, a show that featured Plemons in the role of Todd Alquist.

[20] Director Toby Haynes has previously worked on Sherlock and Doctor Who,[13] and crew from Stars Wars and 2014 film Guardians of the Galaxy were hired.

[12] The spaceship initially uses orange and red colours, and the special effects were made to look like those from the 1960s; a modern version of the ship is shown at the end of the episode, more similar to the 2009 Star Trek reboot.

Plemons watched Star Trek and worked with a vocal coach to pay homage to William Shatner's performance as Captain Kirk.

[10] To avoid building an entire spaceship, most scenes on board the ship were set on the bridge or in corridors; a canteen area was considered but not used.

[10] Production companies Painting Practice and Revolver worked on graphics and the user interfaces in the spaceship,[10] whilst special effects were done by Framestore.

[28] Pemberton wrote a score with elements reminiscent of Star Trek, and other "synthetic and modern" aspects,[30] and some of the music was inspired by Jerry Goldsmith.

[31] A vinyl version of the soundtrack, featuring as its cover the Butcher Billy-designed Space Fleet poster seen on the episode, was released on Record Store Day 2019.

[47] "USS Callister" has been called "the most cinematic episode to date" for the show,[41] due to its use of vivid colours and a huge fictional landscape.

[48] Main character Robert Daly has an unhappy life, where he does not receive credit for co-founding his company and is mocked by workplace colleagues.

[40] As the Captain of USS Callister, he abuses his position of power, forcing his crewmates to act as opposites of themselves, such as Walton going from Daly's superior to his underling.

[49] Critic Alec Bojalad stated that Daly fits an archetype of white males who participate in prejudiced online echo chambers due to social ostracisation in real life and a sense of entitlement.

[16] Likewise, Sonia Saraiya of Vanity Fair called Daly an "incel king" exhibiting "a tired, stubborn form of masculinity clinging to control" with an entitlement to women compared to Cole's feminist fight for her own autonomy.

[49] Tristram Fane Saunders of The Telegraph called the episode "a sharp attack on an entire genre of male-driven narrative" and equates Daly's sexist fantasy involving his attractive younger co-worker with the Harvey Weinstein sexual abuse allegations.

[60] In a negative review, Whitley opined that although the episode has the right number of references, they are used in a "cruel parody and even a misandrous attack on male science-fiction fans".

[62] VanDerWerff compared the crew's escape plan favourably to a "movie prison break",[62] though Franich believed that the fast pace causes the "dull" blackmail of Nanette to be "a too-easy gag".

[48] Bojalad called Milioti's character Cole the "real revelation" of the episode,[45] while Cross stated that she was "painfully easy" to relate to.

[59] Darren Franich of Entertainment Weekly called for Milioti to receive an Emmy nomination for Best Actress for her performance as Cole in the episode.

[87] In March 2024, Netflix announced that a sequel would air as part of the seventh series in 2025, marking the first Black Mirror story to receive a continuation.