The novel All the Bright Places opens with two teenagers, Theodore Finch and Violet Markey, meeting on the ledge of their high school bell tower. Finch, who struggles with depression and often exhibits distressing behavior, spots Violet, who is having a momentary low and wanted to know what it would feel like on the edge. She is scared, and Finch talks her down to safety. Violet is one of the most popular girls in school, but she has been more reclusive since her sister died the previous year in a car accident. Finch is ostracized because of his erratic behavior, and because of the stigma surrounding mental illness. From the moment he meets her on the bell tower, Finch wants to impress Violet and get to know her.
In geography class, he chooses her as his partner for a project that tasks them with discovering sites around Indiana. She is resistant, but eventually relents. Finch pushes her to tell him why she was on the bell tower that day—she tells him it would have been her sister Eleanor's nineteenth birthday, but that the real reason she was there is that nothing matters, everything is just filler until death.
Violet deletes the website, EleanorAndViolet.com, that she and her sister used to have. She has lost her ability to write since the accident, and thinks maybe that part of her is gone. Finch sends Violet rules for wandering—what he has named their geography explorations—and he makes a Facebook account so he can message her. They exchange lines from the Virginia Woolf novel The Waves, which becomes an important book for them throughout the novel. Their first wander is to Hoosier Hill, the highest point in Indiana. They bike there, because Violet still won't drive in a car.
Violet's parents ask her if she was on the bell tower the previous week, which makes her panic, but it's just because a local reporter wanting to interview her called the house. Finch keeps showing up; he bikes Violet to school one morning, and asks her to tell him about the accident. Violet goes on a date with her ex-boyfriend, Ryan Cross, but doesn't have fun. She thinks about Finch, and she hopes he doesn't feel like she blew him off.
Finch finally gets Violet into the car. They go to Bookmobile Park, a set of trailers that each house a different kind of book. They then go to a huge chalkboard where people have written "before I die___." They write in dozens of responses, and Finch's last one is that he wants to kiss Violet Markey. At that point, she wants him to, but she explains it away in the car.
Finch's counselor Mr. Embry asks him if he's been thinking about hurting himself, because he read the list on the school gossip website that named him the most suicidal student. Finch starts walking Violet to all her classes; it bugs her, but he can tell she actually enjoys it. That night, they drive to the bookstore where Finch's mom works occasionally and read from Dr. Seuss's Oh, the Places You'll Go, and then climb to the top of Purina Tower, looking out over the town.
Finch drives to Mudlavia, a spring with alleged healing properties, and drinks down the water, desperate to do anything to rid himself of the pain he feels. Violet adds Bookmarks and Purina Tower to the notebook where Finch asked her to keep recordings of their wanderings. Finch repaints his room—he covers his red walls with the bright blue of a swimming pool, and skips school for a few days.
When he returns, he brings Violet outside during a fire alarm to the river by the school. He shows her a hooded crane, the only in the state, and says he's not lost, he's wandering. Finch swims in the river while Violet writes on the riverbank. When Ryan and Roamer (Finch's sworn enemy) come looking for Violet, Finch and Roamer get into a violent fight.
Violet starts a new website, Germ Magazine. She and Finch drive to the home of a man named John Ivers, who has two homemade roller coasters in his yard. They ride them several times, and on the drive afterward, Violet says she likes that she can talk to Finch. He says he likes everything about her, and then he kisses her for the first time. He wants to have sex with her, but he realizes she is a virgin, and says they will wait.
Finch is feeling better, and even avoided getting into a fight with Roamer. He and Violet spend all their time making out, and when they're not together, they're thinking about being together. They go swimming in the Blue Hole, a bottomless swimming hole, and Finch stays underwater for so long that Violet gets scared and turns angry with him. They have a cathartic moment screaming into the wind and throwing rocks, and when they go back to his house later that day, they have sex.
Instead of bringing her home, Finch drives to the Purina Tower, where they accidentally fall asleep all night. The next morning, Violet's parents are worried sick and furious, and ban their daughter from seeing Finch anymore. Finch, subsequently, descends into a depression: he moves into his closet, and he is becoming more reclusive. In a panic one day, he runs miles to a random farm—it's after hours, so it's closed—and begs them for flowers for his girlfriend. When he gives them to Violet, she says he brought her spring.
Still, Finch isn't feeling well. When Mr. Embry mentions that Finch might have bipolar disorder, he loses it: he doesn't want to be reduced to a label. That day, when Roamer calls him a name, Finch chokes him until he goes purple, and gets expelled. That night, he takes half bottle of sleeping pills, but gets to the hospital in time to have his stomach pumped.
At a meeting of Life is Life, a suicide support group for teenagers, Finch grows more depressed by the unfairness of all these suffering kids. He sees Amanda Monk there, who reveals she struggles with bulimia, and has tried more than once to kill herself. He doesn't tell Violet about the pills or the meeting, but when she eventually goes to his house to check on him, he alludes to his "black moods," and tells her the story of the cardinal that died when he was young. Violet realizes Finch is living in his closet, but he tells her to keep it a secret.
Amanda tells Violet that she saw Finch at Life is Life. For his birthday, he reenacts the Jovian-Plutonian gravitational effect in his closet, which Violet says is the loveliest thing anyone has ever done for her. She tells him that she found out about the support group from Amanda, and Finch's mood turns. They get in an argument, and she leaves. At home, Violet tells her parents they need to help him.
Finch goes AWOL except for a few cryptic messages to Violet. She assumes they are broken up, and is angry with him for disappearing without a word. Violet starts her new website, Germ Magazine. In late April, Finch's sister shows up asking if Violet has heard from him. He sent a cryptic but eery message to his family; he sent one to Violet as well, and to his friends.
Violet pieces together the clues Finch left behind and is led to the Blue Hole, where she knows he will find him, and knows he is dead. When she is asked to identify the body, she says she can't—it looks nothing like the boy she loved.
Violet still has to finish the wandering project, and she wishes she and Finch had recorded more of their explorations. But when she opens the map, she realizes that he has marked the five places she should go. At each place, Finch has left a message for Violet to show that he was there, and the cryptic messages he sent her before linking up as clues to her destination. In the final spot, a church for weary travelers, Violet discovers a note he left her. It is song lyrics, and they tell her everything she needs to know about how much he loves her; finally, she forgives herself.
In the final scene, Violet swims in the Blue Hole, thinking of Finch, and how he will never really be gone. She ponders her own life, and feels ready to see what it has in store.
