Now in its fifth series, Black Mirror has firmly established itself as concerned with theories rather than feelings: as a growing fable collection pondering our futile, fixated romance with technology that doesn’t love us back, it stands to reason that Charlie Brooker’s neo-Twilight Zone creation is predominantly glass-cool rather than skin-warm to the touch. Even its ruminations on human relationships have largely been on the chilly, impersonal side – preoccupied less with the machinations of the human heart than the machines (or simulations) that manage to manipulate it.

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Series three’s San Junipero was a clear, glowing exception. Its tender, shimmery story of a lesbian romance crossing from a real world into a virtual one – and finally, movingly, into a manufactured afterlife – examined outlandish futuristic technology to enable a relationship between sympathetic, flesh-and-blood women, rather than using them as props in a 21st-century parable. Critically beloved and lavished with Emmy awards, it could have been labelled as Black Mirror for people who don’t really like Black Mirror, or as an indication of a clever, slightly clinical series’ expanding world view: by putting two queer female characters at the centre of its narrative, and allowing them to be served by its genre mechanics rather than the other way round, it felt like something of a landmark.

So why does the series five opener Striking Vipers – seemingly fashioned as the fraternal companion piece to San Junipero – feel so hollow by comparison? Like its predecessor, also written by Brooker and directed with ambient eeriness by Owen Harris, the episode studies same-sex attraction as it functions in the real world and a simulated reality where real-world restrictions and prejudices don’t exist. As in San Junipero, too, that attraction flourishes most happily in the artificial sphere. In Striking Vipers, however, the feelings between its part-time lovers appear to change between dimensions – not least because their bodies (and, in one case, gender) are likewise transformed.

Best friends Danny (Anthony Mackie) and Karl (Yahya Abdul-Mateen II) enjoy an entirely platonic relationship for years, growing more amiably distant until a virtual-reality combat game brings them unprecedentedly close. As his fighting avatar, Karl adopts the body of a woman, Roxette, while Danny takes the male form of karate master Lance; the ensuing combat is visceral, oddly arousing, and before long, Roxette and Lance are having in-game sex. Does that mean Karl and Danny are fucking too? Not in person, as their physical bodies remain slumped and separate on the couch while they’re locked into the VR world, but they feel and savour the sensation. Does it count? And if it counts, is it gay, even if Roxette and Lance aren’t?

These are complex questions that Brooker’s script, to its credit, does not seek to answer tidily. Yet there’s a stale whiff of “no-homo” coyness to the way Striking Vipers dramatises two ostensibly straight men’s flirtations with homosexuality and genderqueer indentity. Watching it, I was reminded of nothing so much as Lynn Shelton’s 2009 mumblecore comedy Humpday, a distinctly analogue exercise in which two straight male friends mutually dare each other to make a gay porn film together, each bro calling the other’s bluff until they mutually agree to chicken out. It was an amiable film that nonetheless received an undue amount of discussion for gently returning its characters to heteronormative safety before any serious taboos had been broken, preserving same-sex intimacy as a daunting, sacred final frontier.

Striking Vipers goes further in pushing the boundary between male friendship and something more, though it also positions the VR world as a firm red line in Danny and Karl’s relationship. There, as a heterosexual pair of fighting gods, they are sexually liberated while ironically conforming, on the artificial surface, to social norms; back in reality, an experimental kiss between the two men is mutually agreed to be a non-arousing non-starter. If their body language subtly suggests otherwise, the script lets the matter lie.

As befits the Black Mirror brand, Striking Vipers is fascinated by its fantasy, which is rather ingeniously rendered as a high-kitsch parody of the hyper-macho, culturally dubious Mortal Kombat “orientalism” so prevalent in the video game realm. Yet its human detailing is comparatively skimpy, leaving Danny and Karl scarcely more dimensional than their VR avatars: queer desire is treated, even exoticised, as a disorienting byproduct of alien technology rather than a matter of the heart, while the psychological ramifications of Karl inhabiting a woman’s body to feel sexual fulfilment are glibly grazed over. As ever, Black Mirror excels in presenting big, subversive ideas in a grabby, sexy, hour-long format; for big, subversive feelings to match, however, San Junipero remains its high-water mark.