What are you scared of? The movies love to indulge that question. They say, “Can you imagine the monster waiting, and watching you, in the attic, in the cellar, or in the little house down the lane? I dare you to find out.” The gotcha game is played for fun, and it teases all the real scary thoughts we have. Even in Texas, the whims of politicians are more troubling than the chance of a chainsaw massacre in the backcountry, preying on lost motorists. Texas is not as interesting as that.

But we are all afraid of being lost—we always have been. The grip of Cormac McCarthy’s novel The Road is that of order, grace, and tolerance being lost. A man walks the toxic land alone, having to survive—that is bad enough, but the dread is greater because he has his child, a boy, with him. The fear that haunts most people is the vulnerability of being a parent—you could lose your treasure. Life is easier if you are unattached, but that solitude can drive you crazy. The thing that frightens me is being unable to finish a sentence I’ve begun. (As readers of this column, you may say you know exactly what I mean—or thought I meant.)

In Still Alice, Alice Howland (Julianne Moore) is 50, and a professor of linguistics at Columbia. She lives in the city with her husband John (Alec Baldwin). They have three grown children who are out in the world, to some degree. She is said to be a very good teacher and she lectures to large classes until one day she loses her thread. She goes to a neurologist and discovers that she has early-onset Alzheimer’s. This is rare for someone her age, but it is additionally alarming because the younger you are, the faster the disease moves. Reviews are supposed to leave movie endings unspoiled. But no one is going to go to Still Alice with too much hope. It’s a more effective proposition in the movie business to say the Earth is cracking in two—and of course it is, metaphorically speaking.

Why has Still Alice been made then? Well, its two directors, Richard Glatzer and Wash Westmoreland, found a novel, by Lisa Genova, and they were the more struck by its potential because Glatzer was beginning to suffer from ALS, the neurogenerative disorder known as Lou Gehrig’s disease. The two directors are married, and they made an intriguing movie based on the life of Errol Flynn—The Last of Robin Hood—which flopped. Glatzer was ill as Still Alice was made, and Westmoreland has said that Glatzer’s illness gave everything, “a sense of deeper purpose.” So it should. Alzheimer’s is as daunting a subject as being sent to Riker’s Island or ending up a bag lady on the street. (I knew a screenwriter once who was working on those fates befalling a middle-aged, “successful” married couple.)

I suspect we are in the Stone Age of neurogenerative disorders. We may prove geniuses at dealing with them—though that genius has a long shopping list these days. We may learn that current estimates, of one in 85 people suffering from Alzheimer’s by 2050, are unduly conservative. Maybe we need to know much more about the subject. Nothing except knowledge will spur the research that is required, or support the experience that awaits some of us. So Still Alice is a necessary film, or a step toward an essential process of education. It’s a film about which you will ask yourself, Do I really need to see it this Christmas? That question will be hooked on the near certainty that Julianne Moore will be nominated for her performance. That will be her fifth nomination, and she is an entirely deserving candidate. If our world was founded on the principle of justice.

Julianne Moore is extraordinary at revealing the gradual loss of memory and confidence, and at showing the hulk of physical persistence that remains after intellect and reference have gone. But she is restricted by the destination of this film, and by the flat naturalism of its family life. If this had been an opera, it might be legitimate for the disease to liberate scalding lyrical arias of protest. But dutiful realism cannot go there and instead it asks Moore to mine her weakest resource, that of pained distress. Over the years, looking at The Hours again (and she was nominated for that), I find her would-be suicide irritatingly subdued and locked into the film’s predetermined pattern—its schedule almost—of forms of suicide or retreat. I prefer the actress in Magnolia and Short Cuts where she can burn with anger, fun, and explosiveness.

What I’m trying to say is that Still Alice is not a very good movie, but I’m not sure that it needs to be. Its purpose and its thrust are very close to those of documentary, and one of the most satisfying things in the film, I found, was Stephen Kunken as the neurologist, talking a lot of fact into the picture while being a credibly touched and sympathetic human being. We need to know so much more about this disease, and the plight of the Howland family sometimes feels like mere convenience in that larger cause. So I care about the subject more than I ever did for this family.

That said, there is a smoldering performance to behold. Kristen Stewart plays the Howlands’ problem child, Lydia, who is striving to be an actress. She is still too easily confined by her role as Bella in the Twilight films and by wardrobe malfunctions that the Internet exists to report. It is high time we took her seriously as an actress. This was evident in a few scenes from On the Road, and it will be obvious in the forthcoming Clouds of Sils Maria, where she plays with Juliette Binoche and steals the picture. With little to go on in the script here, she establishes a troubled, sulky energy in the would-be actress who feels desperate for her mother. Stewart may be as good as Julianne Moore, and a day should come when they both have Oscars.