Kate (Hilary Swank) is a classical pianist who is diagnosed with ALS. Her husband Evan (Josh Duhamel) finds out one morning that his wife has fired her previous caregiver, Mrs. Trotter, and that Kate was finding a new replacement. Bec (Emmy Rossum), a wild college student who parties a lot, applies for the job despite her lack of experience apart from having volunteered at a nursing home her grandmother was eventually placed in during her high school years. Kate sees something special in Bec despite her slightly vulgar language and poor housekeeping skills. Yet, despite all the mayhem Bec has caused at home, from messing up the kitchen by blending up a drink without putting the lid on the blender to dropping Kate in the bathroom, Kate maintains a calm and positive demeanor which confuses Bec. One night, Kate has her friends over and finds out that Evan had gone out for drinks instead of dinner unlike what he told her. Later that night, Kate convinces Bec to access Evan’s laptop and they find out that Evan had an affair with his secretary, Cynthia. Distraught, Kate tells Bec to leave, however Bec comes rushing over to Kate’s during a night out in a bar when she gets a text from Kate. Bec finds Kate at the top of the stairs after a suicide attempt where Kate had almost let herself fall down a flight of stairs. Kate then asks for Bec to bring her elsewhere and away from home. They end up staying the night. In the morning she tells Bec to take her to an assisted living home, but Bec refuses to leave her there and is furious that Kate blames herself for ruining Evan’s life with her ALS. Eventually, Kate splits up with Evan due to his brief affair, as well as her wanting not to be invisible after receiving a brief and angry pep talk by Bec.
Bec and Kate have a couple of adventures, including going to a club, meeting another couple where the wife has ALS and trying “herbal therapy.” They eventually go to a party for Kate’s friend’s daughter. Kate asks to hold the baby, but has a coughing fit and almost drops the baby. While Bec is taking care of Kate inside, Evan appears and Kate has Bec tell him her true motivation for leaving, that it was a result of him making her feel invisible. The wife from the couple they met earlier has a complication due to her condition and is hospitalized. It scares Kate when she sees what happens eventually to ALS patients. Bec briefly talks to Kate’s “best friends” who tell her to tell Kate that they love her, miss her, and are here for her. Evan visits the house again, but Kate and Bec turn him away again. Bec’s parents visit for Christmas and a conversation with her Mom that is heard over the monitor by Kate causes Kate to fire Bec because she believes that her illness is ruining Bec’s life like it did with Evan.
Kate goes to her parents’ house and attends a Christmas party with Evan, hinting that they are together again. Eventually, Bec receives news that Marilyn, the other ALS patient they met, has died. She drops off a letter with Evan for Kate that Marilyn sent to some of her friends. Kate becomes hospitalized shortly after and it is discovered that Bec was given medical authority over Kate. Even though Kate’s mother begs her to put Kate on a ventilator, Bec refuses and instead takes her home with Evan. Bec helps Kate play her favorite Chopin piece on the piano again. After Evan professes his love for her, Kate and Bec lie in bed, where Kate makes Bec promise not to call for help tonight and to find someone for herself who can see her. Bec agrees, on the condition that Kate promises to accept a compliment. And Bec thanks her for the Manolos they shared, teaching her how to cook, and letting her experience this with Kate and not letting her mess up this job. Kate dies that night and Bec, unable to stay in the other room, holds her while she takes her last breaths. The movie ends with Bec finally meeting with Will, a nice boy who has been pursuing her, and performing at the club without suffering from stage fright.