Chloé Zhao, fresh off winning two historic Oscars for “Nomadland,” gracefully handles a thankless job with “Eternals,” a Marvel Cinematic Universe origin story that suffers from all the baggy, convoluted drawbacks of the form.

Based on characters created by Jack Kirby that first appeared in a 1976 comic, the latest installment of never-ending MCU hegemony introduces a new, post-Avengers cast of franchise players: the titular band of immortals who were sent to Earth from the planet Olympia thousands of years ago to banish a marauding monster species called the Deviants. With those baddies apparently vanquished, the Eternals have taken on human form, absorbing into normal, everyday life, like so many intergalactic sleeper cells.

When we meet Sersi (Gemma Chan), she’s working at the Natural History Museum in London, keeping her dishy boyfriend Dane Whitman (Kit Harington) at wary arm’s length because of a millennia-old off-and-on thing with Ikaris (Richard Madden). She’s also a surrogate mother to Sprite, a mop-topped tomboy played by Lia McHugh as a disturbing cross between Tinkerbell and a creepy kid vampire from an Anne Rice novel.

When a Deviant unexpectedly fetches up at Camden Lock one evening, it’s clear that Sersi, Ikaris and Sprite have more work to do: Led by Ajak (Salma Hayek), they get the band back together, traveling the world to round up erstwhile allies that, when asked by civilians, are invariably explained away as “friends from college.” The whirlwind tour of locations as far-flung as South Dakota, Amazonia and, eventually, Alaska, mainly serves to give viewers a panoply of backdrops for what invariably turn out to be long, expository speeches questioning why the Deviants have suddenly assumed the ability to heal themselves, and whether humanity is even worth saving.

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Ajak (Salma Hayek). (Marvel Studios/Courtesy of Marvel Studios)

Zhao, whose previous films “Nomadland,” “The Rider” and “Songs My Brother Taught Me” all took place amid the simple majesty of the American West, does her best to imbue “Eternals” with those same sweeping production values: Eschewing computer generated effects as much as possible, she also films in actual locations (England and the Canary Islands), which lends an air of authenticity to a film genre too often hermetically sealed in its own plasticized artifice.

What’s more, she keeps an eye out for small, humanistic moments of intimacy: “Eternals” has been recognized for introducing the first deaf MCU character (Makkari, played by Lauren Ridloff), as well as a gay character and a pluralistic ensemble of actors, but it’s also notable for being the first Marvel movie to feature a sex scene — PG-13 approved, but a breakthrough nonetheless.

From left: Kingo (Kumail Nanjiani), Sersi (Gemma Chan) and Sprite (Lia McHugh). (Sophie Mutevelian/Marvel Studios)

Even with these glimpses of grounded reality, though, Zhao can’t overcome the structural realities of the behemoth she’s been tasked with piloting. “Eternals” is a choppy, whipsawing affair, especially in its first half, when the narrative pingpongs erratically between present-day scenes and those taking place in ancient Mesopotamia, the Gupta Empire and Aztec-era Mexico. Zhao’s script, co-written with Patrick Burleigh, Ryan Firpo and Kaz Firpo, alternates between generic lines like “Run!” and “Watch out!” and leaden, self-serious perorations. There are moments when the visuals of “Eternals” recalls Ray Harryhausen in their adamantly analog effects, and when the heroes work their magic, it often takes on the delicacy of finely-spun scrollwork. But by the time yet another Deviant throw-down arrives with metronomic timing — and by the time the movie begins to sag under its 2½ -hour running time — an inevitable feeling of dull, drearily repetitive predictability sets in.

There are bright spots in “Eternals”: Kumail Nanjiani has a blast as Kingo, who has become a heartthrob of Bollywood cinema and has most of the movie’s best punchlines (one of them is a wink at Thor, one of a few self-referential nods toward what’s happening over in the other ’verse). Brian Tyree Henry is similarly wry as Phastos, who at the beginning of the story has happily given up on superheroics to raise a family with his husband Ben (Haaz Sleiman). As the brooding hothead Druig, Barry Keoghan seethes with Kurtz-like intensity, hiding out in Brazil out of disgust with his inability to save people from themselves; Angelina Jolie plays Thena, a warrior princess now suffering a form of cosmic dementia, with touching naivete.

Ikaris (Richard Madden) and Sersi (Gemma Chan). (Sophie Mutevelian/Photo by Sophie Mutevelian/Marvel Studios)

Thena’s protector is the enormous Gilgamesh (Don Lee), continuing the “Eternals” theme of everyone having an opposite number with whom they can play and riff; unfortunately the most obvious place the gambit doesn’t work is in the film’s central relationship between Sersi and Ikaris, whose exceeding physical attractiveness can’t overcome a fatally inert setup.

As in most launchpads of this type, “Eternals” has so much work to do that chemistry can’t help but get squashed: introducing a seemingly endless cast of characters; putting them into ever-multiplying snares, traps and ambushes; hinting at myriad movies to come and constantly explaining what happened once, what’s happening now and what’s going to happen next. Zhao might have her eye on the nuances, but ultimately even a filmmaker with her sensitivity and vision can’t bend the Great Marvel Imperative to her will.

PG-13. At area theaters. Contains fantasy violence and action, some strong language and brief sexuality. 157 minutes.