Our story starts when an unspecified apocalyptic event kills all humans except one.
Our main character named, Del, is the only person left alive. He used to be a librarian. Even after the world ended, he took care of all the books. He gets his sustenance from food cans in supermarkets. Slowly Del starts to develop a hobby for exploring houses. To keep his mind off things, he cleans each house before looking for pictures and other valuable items. If he found any bodies, he would wrap them and bury them outside. Del marks an X on the map for all houses that have already been explored.
One day while Del was outside exploring, he hears a loud crash and decided to investigate.
Del goes to check on the sound and discovers an alive but unconscious girl named Grace inside a broken-down vehicle. He also finds a gun in her car. He takes her to a random home to nurse her back to health. Sometime later, Grace wakes up with a bandage on her head and discovers that the door to where she’s being kept is locked from the other side by Del. She vomits and has no recollection of what happened the night before.
Del questions her through the door and concludes that whatever happened to him also happened to her. Neither one knows how they survived or why they’re the only people who survived. He tells her he will only unlock the door if she agrees to count to one hundred first. She agrees; however, she immediately breaks her promise and opens the door as soon as Del unlocks it.
Grace begs Del to let her stay with him, and after some back and forth, he finally agrees.
Grace then accompanies Del as he cleans houses and learns his methods. She also realizes that he knows the name of every person who has died in the town. When it comes time to bury the dead, Grace finds it cold of Del not to say anything in memory of them, so she shares that whenever she finds a body on the road, she holds her breath for ten seconds out of pure respect. To humor her request, Del begins doing this with her.
Del sometimes misses the quiet, especially when Grace won’t stop talking.
One afternoon, Grace notices Del isn’t in the library and decides to snoop around his office. She’s shocked to find a whole system of files containing pictures from houses. Weirded out, Grace doesn’t know what to think of it, so she goes for a bike ride to clear her head when she suddenly hears a noise coming from a house and decides to investigate. When she goes inside, Grace is surprised to find a dog that has survived.
She takes the dog home, and all is well for the first few days, but one day the dog ruins one of their books. Del tells Grace to take care of the dog while he cleans up outside, but the dog bites him instead. Grace helps Del clean and stitch up his wound. The following day, the dog is gone, and they look for it around town. After some time, Del finally confesses that he let it out to pee last night, and it probably got lost. Grace believes that he got rid of the dog because he didn’t like it and was very upset.
A few days later, Del wakes up and is surprised to find Grace eating breakfast with two other survivors, Violet and Patrick. When Del asks them who they are, they explain that thousands of other people survived and now live together as a community in California. Del is angry because he feels like Grace has been lying to him this entire time about being the last two people alive on Earth. He leaves in a hurry and ignores Grace’s explanation that Violet and Patrick are not her birth parents.
Later on, Grace left with Violet and Patrick.
Del regrets letting her go, so he tracks her back to her house in California. When he breaks into the house, he sees Grace’s room; She is connected to a machine that appears to be giving her behavior modification therapy to forget about the apocalypse and the loss of her family. Everyone in the community has gone through the same treatment; it is the only way they can move on and be happy again, according to the town’s unspoken rules. Del disconnects Grace from the machine, apologizes for how he reacted before, and then helps her leave. On their way out, they run into Patrick, who tries to stop them from leaving and explains that their system is the best way to move forward. However, Grace takes out her gun and shoots him without warning or hesitation.
At that moment, Violet arrives, and after looking at Patrick’s body with an uncaring expression, she mentions offhandedly about going to look for something to clean up the blood with. Del and Grace ignore her and leave town while looking at the people living their lives with fake happiness. Once they reach the road, Grace tells Del that she is not sorry for shooting Patrick, and Del tells her that he understands entirely while speeding toward their next destination.