Comedy isn't the champagne of bottled beers; it's Champagne, period, a delicate and perfect achievement in itself when it works. That's why it's frustrating when great comic performers feel compelled to prove themselves in what we so solemnly call dramatic roles. The scarily brilliant Robin Williams stumbled into love-me mawkishness whenever he played child-cancer docs and the like. A more recent example is Kristen Wiig: In Liza Johnson's 2013 Hateship Loveship, she turned off every watt of her extraordinary deadpan sparkle to become a drab nanny; as a prim PR honcho in The Martian, she looked lost in space, and not in the good way.

But then, maybe because so much comedy comes from the darkest places to begin with, it is possible for a comic performer to take the quicksilver flash that makes him or her funny and atomize it into something that goes beyond laughter. That's what Sarah Silverman achieves in I Smile Back, Adam Salky's adaptation of Amy Koppelman's novel about a woman — a wife and mother — undone by depression.

I Smile Back is a housewife-crackup drama, though you don't have to be a housewife, or on the verge of cracking up, to respond to it. Salky shows us, in vivid detail, everything Silverman's Laney Brooks has to live for: She has a nice-guy husband (Josh Charles), two no-trouble-at-all kids (a boy and a girl, played by Skylar Gaertner and Shayne Coleman), and a house in the suburbs big enough for everyone to sprawl out in.

Early on, picking up some Chinese take-out, she spots a boy who's having trouble with the utensils and presents him with a set of kiddie chopsticks. It's the sort of thing that a nice mom might do without thinking, in those moments when her brain takes a breather from the hyperconscious job of getting through the day.

But we know early on that something isn't right; perhaps nothing is right. When Laney's young daughter appears with an irresistibly scruffy dog in her arms — “His name is Bingo, and he needs you” — Laney's eyes go cold. The dog is the family's new addition, one she didn't know was being added, but still, her lack of responsiveness is chilling. Laney does normal wife-and-mom stuff one minute, such as packing the kids' lunches with affectionate precision; the next, she's cutting to the bathroom for a line of cocaine. She's sleeping with a guy who's not her husband. She consumes only lollipops and no real food — her husband scolds her for this in front of the children, and she turns it into a wild joke that makes them laugh nervously. She comforts her son after he wakes in terror from a nightmare; one of the dream's key components is that he can't “reach” her because she's wearing earphones, but it's easy to see that, in real life, earphones aren't the problem.

Laney is headed for a fall, and Salky — who has previously directed one feature, the 2009 teen drama Dare — leads us to that point with efficiency that might be mistaken for dull proficiency. What he's really doing, it seems, is creating space for Silverman to spread out, and she fills the picture to its very corners — her performance is the chief reason to see I Smile Back. Silverman has taken serious, or at least semi-serious, roles before, but she's never had a part that demanded so much of her. She has been open about her own battles with depression, but what makes her turn here work is that it isn't nakedly expressive. As a comic, Silverman will say just about anything for a laugh — over the years, her repertoire has included jokes about rape that have been misconstrued but actually land quite clearly on the side of victims. With her onstage comedy, we often don't know whether to giggle or recoil; her skill lies in the way she keeps us suspended in uncertainty, both about her jokes and about ourselves.

But this performance is bold in a much quieter way — there's something veiled and controlled about it, as if Silverman were trying to both reveal and conceal Laney's self-lacerating nature. When Laney snaps angrily at her husband or her lover, the lancet precision of Silverman's stand-up timing comes to the fore. But in the movie's more tender scenes — such as the one in which she expresses the quiet terror that she's passed her depressive nature on to her children, just as she believes she's inherited it from her own absentee father (played, in a small, sharply wrought scene, by Chris Sarandon) — Silverman shows us a person we've never seen before. She's playing a character, not stroking her own neuroses; she's too much of a pro for that.

Robin Williams wasn't the first comic — nor will he be the last — to reveal that it's the funniest people who are often hiding the most. (Judd Apatow tried to mine that idea, with middling success, in his 2009 Funny People, in which Silverman briefly appeared, playing herself.) Silverman's openness seems healthier. As a comic, her neediness is both self-evident and no big deal — she frees us to laugh at her without having to worry deeply about her psyche. And as an actor, she draws from whatever darkness is inside her without steeping in it. It also doesn't hurt that she's one of the great, offbeat comic beauties: Her features are as mobile and expressive as a James Thurber cartoon, only finer and prettier, and they're matched perfectly by that vaguely heliumized voice.

In I Smile Back, we both cringe from Laney and reach out to her. The only thing we don't do is laugh at her. That would hurt too much.

I SMILE BACK | Directed by Adam Salky | Written by Paige Dylan and Amy Koppelman, based on Koppelman's novel | Broad Green Pictures | Sundance Sunset

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