English professor Melina Kroner is walking her dog, Vigo. She crosses the street and a black car almost hits her. She knocks on the hood but the driver ignores her and drives on. As she continues on, a city bus for "Route 63" appears ahead of Melina. The doors open and Vigo pulls at his leash trying to get on. The driver looks out invitingly but Melina pulls Vigo back and moves away. However, when she turns back a few seconds later, the bus has disappeared without a sound.
Melina returns home and looks at her engagement and all the photos of her happy life, including her fiancé Adam. Adam comes down and asks if she's okay. A worried Melina wonders if they have a bus route in their neighborhood. The next day she meets with her mother Devora to prepare for her upcoming wedding. Devora can't find any record of Melina's wedding registry and Melina doesn't remember who she set it up with. Later, as she walks her dog a strange woman addresses her by name. The same Route 63 bus pulls up and the passengers look out at her. Vigo pulls at his leash to try to get on board but Melina pulls him away.
That night at home, Adam asks her what's wrong. She tells him what happened and points out there's a bus bench in front of their home that wasn't there before. Adam takes her out to look at it but doesn't find anything suspicious. As they go inside, Adam starts to go into the wrong apartment but figures he's had a little too much to drink.
The next day, a student quotes Emily Dickerson and death from Melina's class and thanks the teacher for helping her. Afterward, Melina calls the transportation department, who inform her there is no Route 63. She goes back to her home and sits on the bench outside. Adam comes looking for her and Melina talks about how she's starting to forget things like how they meet in college. He wonders if it's some kind of test. She goes inside but when she washes her face, a wound on her forehead appears and drips blood all over. A second later it's gone. She hears the bus outside and runs to confront the driver. He simply looks at her and she asks what he wants. The driver tells her that they're waiting for her. Melina tells him to leave her alone and he smiles sadly, then gets in the bus and drives away.
Melina meets with her mother again and explains what she thinks is happening: she died in the car collision the other night, and the bus is Death trying to claim her. Devora is understandably skeptical but Melina is worried that if she gets on the bus, she'll die for good and lose the happy life she has. Devora tells her to get a hold of herself but Melina sees the bus outside. Her nose starts to bleed but when Devora comes, the bus and the driver are completely normal.
Melina calls Adam to meet her at a diner and tries to explain what she thinks is happening. However, she discovers that she can't remember meeting Adam in college. Instead she thinks he moved in next door and that's how they met. She goes to the counter to get coffee refills and the girl there recognizes her. Melina has no idea who she is and the girl says that Melina works there and trained her. Melina angrily insists she's an English professor and asks for two refills. The girl points out she only has one cup. Melina turns in horror to discover that Adam ha disappeared.
Melina runs home and discovers that all the photos of her and Adam are gone, and her engagement ring has disappeared from her hand. Vigo runs outside to where the bus is waiting and gets onboard. The driver is there and strokes the dog, then invites Melina on board. She refuses and the driver sadly notes that the bus isn't Death: it's Life. The life she's been experiencing is the life she could have had. He drives away and Vigo looks sadly at his mistress.
As the bus leaves, Melina sees herself and Vigo lying in front of the car that ran them over. The neighbors have gathered, including Adam and a blond girl that is his fiancée in this life. Vigo suddenly comes back to life. None of them remember very much about Melina: a solitary girl who worked in a local coffee shop and never talked to them. As Adam walks right through Melina, she realizes as she starts to fade away that the bus was her chance at taking back her life and finding a new happiness… and she chose not to.