• Shades of Grey: Turner and Chastain do their best to look iconic in Kinberg's tired, muddled version of a classic X-Men story.

What can you say about a twentysomething girl who suddenly acquired the power to destroy the world? That she was beautiful. And a Mutant. That she loved some guy (Tye Sheridan) who spent the entire movie wearing a visor, though we never found out what they saw in each other. That she caused a lot of A-list actors to wring their hands, and then things exploded, and then the movie was over. But Jean Grey, aka the Dark Phoenix (Sophie Turner)? We never knew her at all.

If I'm doing a riff on Erich Segal's Love Story, it's because the latest X-Men movie likewise asks us to take the lovability of its heroine on faith. Technically, this is the fourth film in the prequel/reboot series that started with the far superior X-Men: First Class (2011), and the third time writer-director Simon Kinberg (X-Men: Apocalypse) has adapted aspects of Marvel's The Dark Phoenix Saga. That cycle is renowned among comics fans for its portrayal of a beloved character's descent into darkness.

But Jean hasn't played much of a role in the preceding films, and Dark Phoenix fails to establish her as a character we care about, let alone a beloved one. The result is a muddled movie that makes hash of the story fans expect without serving up much for casual viewers to enjoy, either.

A prologue establishes that Jean's telepathic and telekinetic abilities played a role in the accident that left her an 8-year-old orphan. Professor Charles Xavier (James McAvoy) gave her a home at his school for Mutants, but apparently he couldn't assuage the rage within. After a mysterious cloud of space energy supercharges Jean's powers, she goes Carrie on her former teammates and mentor, egged on by an alien (Jessica Chastain) with an agenda of her own.

The thing is, Stephen King showed us exactly what Carrie White was exacting vengeance for. In Jean's case, it's harder to say. Dark Phoenix's hand-wringing goes into high gear when the other X-Men learn of Xavier's paternalistic treatment of child Jean and mount a long-brewing challenge to his leadership, spearheaded by Raven (Jennifer Lawrence, phoning it in). Yet Xavier's sins are so foggily delineated that the operatic angst feels unearned. With almost no scenes to establish her perspective, Jean comes off as a spoiled adolescent raging at Daddy.

If Captain Marvel proved one thing, it's that aliens characterized solely by their haughty disdain for Earthlings make boring antagonists. For all Chastain's efforts to be slinky and sinister, she lacks the campy charms of Ursa in Superman II, and her motives are vague at best. If one cast member manages to rise above the dull, humorless screenplay, it's Michael Fassbender as Magneto. He does most of his acting with his hands, raining metal debris on his enemies with the gusto of a conductor leading an orchestra; that, at least, is fun. Even better, he has a henchman who attacks with killer braids that dart like snakes.

Dark Phoenix demonstrates the obvious: We don't care about our heroes "going dark" unless we already know them in the light. There's a reason the makers of the Avengers movies gave us all those drawn-out origin stories. Here, a few sharply written scenes might have sufficed to clarify Jean's character, but she remains an icon in search of a personality. Love may mean never having to say you're sorry, but someone should be sorry for this mess.