With ‘I Smile Back’, Sarah Silverman joins the legion of comedians who have stripped away their funny to deliver a straight and dark performance that showcases the tears behind the smile.

Sometimes, that can be an annoying career transition for comedians more interested in trying something new than actually committing to the difficulties of delivering a challenging performance. Thankfully, ‘I Smile Back’ isn’t one of those movies. It might not be a perfect film, but Silverman’s performance is dead-on and should change the way many people see her.

Silverman stars as Laney, a suburban New Jersey mother with a secret life that has more in common with ‘Bad Lieutenant‘ than Martha Stewart. The film opens with her dropping her two young children off at school before snorting down some drugs, popping out to a hotel to bang a family friend, and engaging in a barrage of self-destructive behavior before bottoming out by doing something fairly disturbing in her daughter’s room while she sleeps. Luckily for Laney, her ridiculously supportive husband (Josh Charles) is something of a self-help guru, so he happily ships her off to rehab after her latest spiral. Eventually, Laney returns and tentatively tries to return to her life, but to anyone paying attention it’s clear that she’s a ticking time bomb.

Silverman is absolutely remarkable in the movie. She’s long seemed more gifted as an actor than the limited roles she’s been stuck with could show, and dives in fully here. Aside from a handful of moments where bursts of her sarcastic humor slip out, she’s completely removed from her usual persona. Even when she flashes her smile, it’s clearly concealing pain or has been put on to manipulate. Despite engaging in fountains of inappropriate behavior, Silverman clearly empathizes with this lost soul and tries to present her as honestly as possible, even when most viewers will want to turn away. Her casting might be a stunt to a certain extent, but that stunt paid off.

Apparently, director Adam Salky and his writers Paige Dylan and Amy Koppelman conceived the film specifically for Silverman, so they can all be credited for seeing something no one else did. That’s likely their biggest contribution to the movie. Though the film is well made and the script is admirably harsh, it’s also essentially limited to being the Sarah Silverman show. No other characters get to develop much of a life beyond how they interact with the anti-heroine, and the few times the filmmakers try to explain her binges of bad behavior can feel uncomfortably flat.

‘I Smile Back’ doesn’t do much beyond present a horrible lost character, warts and all, and let the audience decide what to make of her. Yet thanks to Silverman’s remarkable performance, the film delivers on that single task fairly well. It works, just don’t expect to walk out of the theater feeling particularly wonderful about anything.