Some spoilers ahead.

Introducing Noah at the New York City premiere Wednesday night, Darren Aronofsky promised the audience would see Emma Watson as they never had before. About an hour into the massive Bible epic, when Watson’s character, Ila, is healed by Methuselah (Anthony Hopkins) and sent into a fit of lust, that seemed like a massive understatement. Hermione in filthy robes, copulating on the floor of a forest? What witchcraft is this!

But Watson isn’t another child star getting down and dirty for the sake of being seen as a grown-up, as she’s already proven with an impeccable string of roles in the post-Potter years. What’s different in Noah is that Watson gives the kind of mammoth, earth-rattling performance that grown-up careers are built on. In a cast full of heavyweights doing capital-A acting, including Oscar-winners Jennifer Connelly and Russell Crowe as her parents-in-law, Watson anchors the film’s rawest emotional scenes. In a movie that contains the actual, literal word of God, Watson is handed the stirring final monologue. (Spoiler alert: they survive the flood. Humanity re-populates.) Sitting on an Icelandic beach with Russell Crowe, her hair wild and eyes burning, Watson is quiet but ferocious. In Noah, we watch a lot of people endure unbearable things; with Watson, we actually feel it.

Watson’s role is, in some ways, the typical long-suffering wife, a woman stuck in a rough and patriarchal society and, eventually, on a boat with a father (Crowe’s Noah) who is increasingly unhinged. Ila was orphaned and raised as Noah’s daughter, but she’s also taken up with adoptive brother Shem by the time the ark had neared completion. (Not a lot of options in those antediluvian days.) When her barrenness is cured by Methuselah and Ila becomes pregnant, it’s in direct contradiction to what Noah now believes is God’s plan: for humanity to die off the earth entirely.

Watson has to do a lot of crying in the role, from fights with her crazy father-in-law to a brutal childbirth scene. Actors are often given too much credit for indulging in huge emotions, but it’s not Watson’s tears that are impressive; it’s where they get her. Having survived the ordeal and lived to see the world reborn, Ila emerges as the toughest among a remarkably hardy group of people. The movie is still about its title character and his conversations with God, but when Noah is overcome by doubt and possible madness, Ila takes over the job of piecing the world together again. The girl Noah once considered a disposable burden has become the only possible guide toward the future.

That kind of reversal is common in many stories—the meek shall inherit the earth, after all—but it comes as a surprise in a giant movie called Noah; even our modern conflicted antiheroes, from Batman to Walter White, tend to get the last word in their own sagas. Aronofsky and his co-writer, Ari Handel, structured the story that makes Ila a heroine, but Watson elevates it, becoming the film’s moral anchor so elegantly we barely notice it happening. It’s a big, sometimes broadly defined performance—all that crying!—but Watson finds the smallest details to make Ila a person, not an idea. No easy feat in a story that’s one of the original myths.

Young heroines generally come in stories explicitly built around them—Katniss, Tris, Lyra, Meg Murry, Ramona Quimby, etc. One of the rare exceptions, it turns out, is Harry Potter’s Hermione. As a child, Watson was precocious and engaging, but it was hard to know if that steely, brainy appeal would translate into adulthood. In Noah, Watson steps confidently from the floodwaters into full-fledged movie stardom.