Acting is the art of the inscrutability of the self. If, as Sartre would have it, the other person is unknowable, and, as Grotowski said, “no one can know the mind of the other person,” then it is the actor’s conundrum to know the mind of the person she plays and make him knowable to us, when we see her before us. Philip Seymour Hoffman was such an actor; we knew the persons he gave us more than those in our actual lives; he peopled the world, as Strindberg might have said it, with souls. But there is another sort of actor, the kind who knows that the person is unknowable even by herself, and gives us a soul so companionable, yet infinitely unknowable, that it might be a person in our own lives, someone we know, or might want to, or, for that matter, not to.

No one in the movies intuits this more than Rooney Mara. The truth of the persons she creates is that I have never been able to grasp them. They can be liked, desired, loved, understood, even, in the quotidian sense, but they cannot be known. It’s not what they are that makes them real, but the blanks in between. Therese in CAROL, the Todd Haynes film from the Patricia Highsmith novel The Price of Salt, is the latest she has given us, a young woman we know a little better than she herself does, because we have some idea of her future, but whom neither we nor she can know fully. She seeks the most basic agency, which is self-knowledge, yet knows it will never be more than a provisional understanding. There is a line in the film, taken from the novel, that describes just how odd a “girl” she is for knowing this, so pivotal that it would be a spoiler to quote it, but so apt that hearing it, spoken by Cate Blanchett, as Carol, feels like vertigo.

Carol walks into the Manhattan department store where Therese works, as Christmas help, at the doll counter. It is 1952: we’ll hear a bit of Eisenhower’s inaugural when January rolls around. The red caps the shop girls wear – Therese has to be reminded to put hers on – are diffident splotches on a famously grey decade. Blanchett, in the title role, is a different sort of actor than Rooney, and Carol is a different sort of part. It would never occur to her to ask who she is but instead what to do in response to whatever, in or out of her control, happens. Therese is attracted to her from across the room in the way a stray cat sniffs out the animal lover who will feed her. But it’s Carol who comes to her, asking after a doll for her daughter. We learn, in a clever bit of dialogue not in the novel, that Therese didn’t like dolls as a girl, but preferred trains. So begins a quest on the part of Carol to follow a desire and on Therese’s to embrace a self she has yet to meet.

Todd Haynes makes very good movies and so do the novels of Patricia Highsmith. Hitchcock’s film of her Strangers on a Train and René Clément’s Purple Noon, based on The Talented Mr. Ripley, are undisputed classics. So, probably, is Minghella’s The Talented Mr. Ripley, which made overt the homoeroticism implicit in her books and the perversity of its repression. The Price of Salt is one of only two Highsmiths in which the homosexual theme is both primary and explicit (the other is Small g: A Summer Idyll), and it was first published under a pseudonym, but in other respects it fits neatly into her canon. There’s a sense that anyone could do anything, anytime, of being watched, threatened, invisibly stalked, prey to the biology of an amoral species. The Price of Salt has all of that, with more detective story touches than might be expected from a novel best known for its place in lesbian fiction. It is now, from Haynes, one of the best films that he, or any of her books, has made.

Phyllis Nagy’s screenplay, using the novel’s alternate title, tracks the book with just a few well-considered alterations. It is framed as flashback, from a late point in the story, which reminds us that CAROL is, for us, a flashback to another time. The persons and events connected to the department store are fewer, the road trip is cut short, and the detective elements are truncated (never has Chekhov’s gun been so summarily dismissed). Therese is made, ingeniously, into an aspiring photographer rather than theatrical set designer. The photos enact her search for an elusive self, her own and Carol’s, and become part of the film’s visual texture, the black-and-white imagery a counterpoint to Edward Lachman’s softly colored cinematography. They deepen the intensity of Mara’s gaze, around the directness of which CAROL is in many ways built: indeed, it is the force of her eyes that brings the film to its end.

The pace and imagery of Haynes’s filmmaking captures the comforts and conformities of mid-century Americana: the Manhattan lunch spots, sedate living rooms, city hotels, diners, cars, and motels. Carol, the affluent, divorcing mother in a custody fight involving a “morality clause,” takes Therese, the artistically inclined shop girl, on a holiday road trip, to the distress of her consternated boyfriend, and as they pull out, you hear one of those commercially drenched Christmas carols that were part of the texture of the era. CAROL has, like Haynes’ Far from Heaven, also about a ’50s forbidden love (mixed race rather than same sex), the feel of a Douglas Sirk movie. It’s so evocative of the period that it could make you nostalgic for the ’50s were it not for the prejudices on display, and for those who actually do want to go back to them, and not because they saw CAROL.

But it is, frame for frame, the acting that makes CAROL a great film; of these two, together, there is never enough. Blanchett is at her bravest and most nuanced. In the scene with the lawyers, when a roomful of men are telling her to be quiet and go along or lose her child, she makes of Carol a sort of lesbian Nora, quieting them, insisting they listen, and going, the Christmas door slam of Ibsen’s Doll House reconstituted. Carol needs, and deserves, this moment. In the novel, she is a rather disagreeable figure, not for any bad behavior, but because she is both self-centered and a little dull; yet something in her upends Therese’s world: you know it in the film by the fixity of Mara’s gaze. Blanchett gets the dullness, but also whatever it is that Therese “sees in her,” undefinable, but there, glamorous, and, to Therese, unique, and new. Therese’s senses are enlivened, and Mara makes her, in all her mystery, of infinite substance. Blanchett makes Carol lush, and covered in luxury, befurred and smelling of perfume. You feel, when CAROL is over, as though you have touched her. Salt is, after all, the taste of skin.

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