When an actor boards a star vehicle, they’re generally pretty certain where they want to go: awards central, via kerching alley. So it makes you wonder what destination Jennifer Aniston requested when she hopped aboard Cake. Here is a movie that exists solely as a showcase for hitherto hidden acting chops; an anti-vanity catwalk down which she can limp, drained and hideous. But it won’t win awards, because it’s – admirably – light on histrionics; just a humdrum yet hokey study of the effects of chronic pain. Nor will it make any cash, for it’s about as fun to watch as sciatica. You just hope it was fun to make.

Aniston is Claire, whom a car crash has left with scars on her face and body and constant agony in her legs and back. More than that, perhaps, it’s rendered her permanently pissy: short of fuse, forever of headache, sleepless, no fun, low on compassion. Everyone is giving up on her: her husband (Chris Messina), her physical therapist (Mamie Gummer), her support group, which asks her not to return after she makes inappropriately congratulatory remarks about the suicide of one of the members, Nina. Claire’s one constant is housekeeper Silvana (Adriana Barraza), who is still up for taking her to Mexico to stock up on drugs, and turns a blind eye to her transactional sex with the married gardener. Aniston fans be warned, though: this is sex in sweatpants, carefully positioned, a brief but not complete relief from agony, and from her persistent bitching.

Then Claire starts seeing visions of Nina (Anna Kendrick), who, like an airbrushed Elvira, urges Claire to follow suit and chuck herself off a motorway bridge. Instead, she seeks out Nina’s grieving husband (handily hunky Sam Worthington) and his young son. Along the way, there are distracting cameos from the likes of Lucy Punch, Felicity Huffman and William H Macy, and a redemptive arc you could trace with your eyes shut.

Aniston’s drab-act is diverting, but it’s not enough to sweeten a character who is one hell of a pill. Was Claire at some point in the scripting supposed to be less crabby, more winning? Press material describes her as “acerbic” and “hilarious”, of which only one is remotely true. Despite its sour centre, Cake’s conceits quickly crumble, leaving just a half-baked pity.