"Still Alice" portrays with consummate dignity the harrowing effects of an undignified disease. More than that, it is the unshakably forthright story of an able-bodied, thought-flourishing woman who learns she will one day, very soon, no longer know who she or her loved ones are. Beautifully written and directed by Richard Glatzer and Wash Westmoreland (2014's "The Last Days of Robin Hood"), adapting from Lisa Genova's best-selling novel, the film's unsuspecting page-turner quality derives from its unforced, piercingly true observations rather than contrived gimmicks or plot points. The results are ceaselessly absorbing and uniquely haunting, shepherded by what could quite possibly be a career-best performance from Julianne Moore (2013's "Carrie")—no small claim for an actor who consistently works at the top of her game.

Dr. Alice Howland (Julianne Moore) has just celebrated her 50th birthday. She has a supportive husband, John (Alec Baldwin), close relationships with her three grown children, and is a well-respected linguistics professor at New York's Columbia University. If her life isn't perfect—no one's is—she is prospering personally and professionally, doing what she loves. Her scattered bouts of forgetfulness are minor at first—she occasionally has to search for a few seconds for the word she wants to use, or has to consult the written recipe for a bread pudding she should know by heart—but quickly increase in severity. When Alice goes for a jog and briefly loses her way on the route she always takes, she knows something is terribly wrong. The diagnosis is early-onset Alzheimer's, and, even worse, there is a good chance her kids have genetically inherited it. For a woman who has always valued her own intellect, the emotional blow of realizing her mind is failing is close to unfathomable. If she had cancer and saw her body deteriorating, it would still be awful but at least she would remain herself until the bitter end. To be physically healthy in every way but inside her brain is a vicious insult that crushes her to the core.

A deeply moving character study told from a devastating but not pitiable angle, "Still Alice" refuses to flinch from its title protagonist's reality. The film sees her in all her various peerless shades and layers as the woman she is, and the one she becomes. For as long as she can, she wants to be there with, and for, her kids—lawyer Anna (Kate Bosworth), who has recently announced she is pregnant; middle child Tom (Hunter Parrish), a med student; and youngest Lydia (Kristen Stewart), an aspiring actress in L.A. who has yet to receive her big break. When the time comes and Alice no longer knows herself, she has made a video for herself on her computer with directions to swallow a bottle of pills hidden in a dresser drawer upstairs. There is no telling if this plan will work, but she wants to cover her bases. Until that time comes, Alice tries to continue working—a prospect easier said than done for a professor specializing in words—and when she no longer can, she turns her attention to preparing a speech for an upcoming Alzheimer's conference. This latter scene, with her son and doctor (Stephen Kunken) in attendance, is exquisitely handled. When she mixes up her notes while in front of the audience, the viewer shrinks down, nervous for her and the situation's potential contrived manipulations, but directors Glatzer and Westmoreland carry it through with empathetic grace.

Julianne Moore (2013's "Carrie") is brilliant as Alice, a lofty adjective but a necessary one in this case. How Moore immerses herself in this richly developed, emotionally demanding role is astonishing to behold, and she never once steps wrong navigating her character's full journey as the illness begins to swallow her up. This is no sudsy disease-of-the-week melodrama, either, but an uncompromising slice-of-life that sees Alice—and the life she has built and stands to lose—as so much more than a woman with Alzheimer's. Her relationship with husband John, becoming strained but remaining loving, strikes as readily authentic, a late scene where the two of them stop to get frozen yogurt together breathtaking in how simple yet shattering it is. Alec Baldwin (2013's "Blue Jasmine") is simply terrific as John, he and Moore building a history for their characters that can be read in every one of their lived-in interactions. As Lydia, Kristen Stewart (2012's "Snow White and the Huntsman") is note-perfect, hopefully putting to rest any of her narrow-minded naysayers who refuse to see her as anything more than Bella from the "Twilight" series. Lydia and her mother share hints of contention between them—Alice worries than acting is not for her, and cannot help revealing the concerns she has—but there is a true bond and affection that is readily apparent, as well. When Lydia gets a job performing in a theatre near the family's Long Island beach house and her parents and siblings come to see her in the play, Stewart's subtle yet expressive face shows every last painful thing she is feeling when Alice comes up to congratulate her and has to be reminded of who she is.

"Still Alice" reaches an ending that is neither final nor exploitative, closing on what matters most: the unyielding connection between loved ones. If Alice is unable to hold onto herself, her family remembers who she really is and was, and no debilitating neurodegenerative disease will be able to take that away from them. Perhaps this sounds like a tough motion picture to sit through, one that is grim and exhausting. For sure, this isn't lighthearted fare, but the amount of radiance and resilience the actors and filmmakers bring to each moment makes the experience of watching it an immensely satisfying, even comforting, one. On top of that, Julianne Moore's lead turn is towering and momentous, the work of an actor whose awe-inspiring natural talent knows no limits. Watching her in this role provides a thrill that not even some of the best action films could hope to attain.