High above the chaos of Cannes’s Croisette, in a silent hotel suite at Le Majestic, Lily Gladstone is making Earl Grey tea. Dressed in a crisp white suit and speaking in low, hushed tones, she looks perfectly serene—too serene, certainly, for someone who’s gone from relatively unknown indie actor to an Oscar frontrunner virtually overnight.

In Killers of the Flower Moon, Martin Scorsese’s sweeping crime saga adapted from David Grann’s non-fiction tome of the same name about Oklahoma’s oil-rich Osage community whose members began to die under mysterious circumstances in the 1920s, she gives a commanding performance that towers over everyone else’s—no mean feat, considering her scene partners include Robert De Niro and Leonardo DiCaprio. They play Bill Hale and Ernest Burkhart, an uncle and nephew who covet the extraordinary wealth of their Native American neighbors and hatch a plan to carve out a piece of it for themselves, setting their sights on the single and prosperous Mollie Kyle (Gladstone).

She spots their scheme a mile off, and yet she falls for Ernest anyway, drawing him into her world, teaching him the Osage language, and even helping him dress the part. Once the pair marry, though, she begins to weaken—firstly from her heartbreak at losing several family members to the so-called reign of terror, and then from the diabetes which is ravaging her body, made significantly worse by the insulin shots Ernest insists on giving her.

His crimes, as well as Bill’s, are eventually exposed by FBI agent Tom White (Jesse Plemons)—in fact, an earlier version of the script centered on him before the focus shifted to Mollie and Ernest—but, despite her ailing health, it’s Mollie who seems all-powerful. Still and stoic, Gladstone appears to carry all of the pride and pain of the Osage in the stiffness of her spine, the gentle way she folds her hands together, and the expression of deep and profound melancholy in her eyes.

The 36-year-old Native American actor, who worked alongside countless Osage performers in the film but is herself from Montana’s Blackfeet Nation, has delivered moving turns in Kelly Reichardt’s Certain Women and Sterlin Harjo and Taika Waititi’s Reservation Dogs, but this is unquestionably the role that will change her life. As her awards campaign kicks off, she tells us about the unimaginable strength of the real Mollie, shaking in the presence of DiCaprio and De Niro, and how she’ll approach the next few months as the buzz continues to build.