Jennifer Aniston in Cake.

Jennifer Aniston personifies emotional and physical pain in Cake. She does such a great job of looking and sounding miserable that it wouldn’t be surprising to hear that crew members were driving nails into her feet out of the camera’s view during takes.

Aniston plays a woman named Claire, and the reasons for Claire’s misery are not made clear until well into the film, a wise choice by director Daniel Barnz and screenwriter Patrick Tobin. Not only does this slow revelation provide the film with some decent mystery; it allows the focus to solely be on Claire in the moment, as she struggles with physical back pain and some sort of loss.

The film opens with Claire in a chronic-pain support group. They address the loss of Nina (played by Anna Kendrick in photos and flashbacks), a member who committed suicide by jumping off a freeway overpass. Claire makes a brutally honest observation about the conditions of her suicide—and gets ejected from the group. It’s clear that Claire is a dangerously unhappy person.

Little is revealed about Claire’s background as the film progresses. We learn she has a husband (Chris Messina) who cares deeply for her, but no longer lives at their house. She appears to be taken care of financially, with a supportive housekeeper, Silvana (Adriana Barraza), who endures her mood swings.

For unexplained reasons, Claire fixates on Nina, sometimes dreaming about her, and even hallucinating about her after indulging in too many painkillers. Her obsession leads her to Nina’s house, where she meets Nina’s widower, Roy (Sam Worthington), and her son. Worthington delivers perhaps his best performance yet as a man who is confused by the loss of his wife, and who deals with Claire in a curious, yet amiable, way.

The relationship between Claire and Roy is unorthodox, yet delicately handled. I’ll dare to say it’s even charming, which is surprising, considering their emotional states. Aniston and Worthington are both very much in command of the raw emotion and pain in play between their characters. They even manage to inject a fair amount of humor.

Aniston manages to make Claire a sympathetic character despite her constant unpleasantness. While we only get glimpses of the Claire that might’ve existed before her back and heart became racked with pain, it’s obvious that Claire was once somebody for whom many people cared—and she pushed them away for solid reasons. The pain of her losses never leaves Aniston’s face, even when she is smiling.

Aniston has played dour people before—and she’s played them well. (For example, check out her performance in The Good Girl.) I’ve always viewed her as very talented, so her effectiveness here doesn’t surprise me.

Even though we do find out some of the reasons behind the tragedies Claire has endured, many of the details remain shrouded. Some critics have found this frustrating, and punished the film for it. I think it’s one of the film’s many virtues. Not knowing exactly why Claire is in pain somehow makes her struggle all the more vivid and compelling.

The excellent supporting cast also includes Felicity Huffman as Claire’s therapy-group leader. Huffman has a couple of great scenes, including an odd one involving vodka. (Her real husband, William H. Macy, makes an important cameo.) Mamie Gummer (Meryl Streep’s daughter) is also very good as a physical therapist who has had enough of Claire’s shit.

You’ll probably want to watch a couple of Friends episodes after taking this one in, if only to see Aniston happy and pain free again. Cake is a good movie—but it’s a rough one to watch at times. Just like it should be.

Cake is now playing at the UltraStar Mary Pickford Stadium 14 (36850 Pickfair St., Cathedral City; 760-328-7100), the Regal Rancho Mirage Stadium 16 (72777 Dinah Shore Drive, Rancho Mirage; 844-462-7342) and the Century Theatres at The River (71800 Highway 111, Rancho Mirage; 760-836-1940).