Theodore Finch suffers from an undiagnosed bipolar disorder. As he narrates his story, he tells the reader that he thinks about suicide every day. This is his first week back at school since November, as he experienced a long-term blackout. He counts the days since he “woke up.”
His older sister covered for him and told the school he had a severe case of the flu. His mother is unaware of his psychological problems and did not know he had missed so much school. Finch has no idea what happened over the holidays. This is his first week back after the winter break. He finds himself in the school’s bell tower, contemplating suicide again, and discovers he has company, Violet Markey.
When students below notice them, Finch pretends that Violet climbed up to save him. He quietly talks her down, even as the crowd grows below them. Once they are safe, Violet thanks Finch, but asks him not to tell anyone the truth.
Mr. Embry, the school counselor, calls Finch to his office. Finch convinces Embry that he was not considering suicide, but the counselor still wants to talk with him twice a week, just to be sure. Finch explains to the reader that he contemplates suicide not because he wants to die, but because he wants to have control of his life. He does not want to black out again.
Violet is counting the days until graduation. She has been depressed since the death of her sister, Eleanor, in a car accident the previous year. Life now has no meaning for Violet. She refuses to ride in a car and feels guilty for the occasional moment when she laughs or enjoys herself anymore. News circulates around the school that she saved Finch from committing suicide, and she does not deny it.
Finch and Violet are in the same geography class. The teacher assigns a special project, one in which students must pair up and find unique places in their home state of Indiana and make a report. Finch insists that he and Violet work together. She tries to convince the teacher she is not emotionally ready to do the assignment, but the teacher tells her it is time she stopped making excuses.
When Finch gets home that afternoon, he does something he swore he would never do and signs onto Facebook. He sends a friend request to Violet. She accepts it and sends an angry message about how he ambushed her in class, forcing her to do the assignment. He types a pithy response in which he extols the wonderful opportunity they have to explore the little known places of Indiana and find an adventure in it.
Violet does not respond. He makes up rules for their project. They have to use maps, not apps. They will take turns deciding where to explore, and they must leave something at every place they go.
As Violet and Finch begin, Finch has a crush on Violet and is eager to help her see the joy in life. Violet is intrigued by Finch’s eccentricities. He is highly intelligent, yet not a nerd. He changes personalities — pretending to be an Australian exchange student one day and a boy from the 80s the next day. Their exploration of Indiana starts with a bike ride to Hoosier Hill, the tallest point in the state. Although they are only required to visit two locations, Finch circles many more towns on the map that he wants to see.
As Violet begins to trust Finch, he is able to drive her to the next memorable place. It is the first time she has been in a car since the accident. Violet has picked The Bookmobile Park to visit.
They spend a wonderful few hours visiting the different trailers of books. Finch tells her that they must pick still another spot to visit as this one was too close to their town. He finds ways to be around her at school, even though they only have one class together.
He wakes her up in the middle of the night by throwing pebbles against her window, and then takes her on impromptu visits to the bookstore his mother owns so they can read Dr. Seuss’ Oh, the Places You’ll Go! Violet finds herself wanting Finch to kiss her, but he refrains.
Finch begins to descend into one of his dark periods again. He skips school to repaint his room. As his walls were a deep red, it takes several days for the new blue paint to cover the color. When he returns to school, he pulls the fire alarm so that he and Violet can leave school together and hang out by a river.
Finch goes skinny-dipping, while Violet writes about this new adventure. After Finch is dressed, several of Violet’s popular friends find them. One of them, Roamer, has been an enemy of Finch’s for several years. Roamer punches Finch several times before Finch finally defends himself by shoving Roamer’s head underwater.
Violet’s parents become concerned when they learn she skipped school after the fire alarm. They worry that Finch is a bad influence on her. Her mother, a writer, encourages Violet to start a new online magazine since she had success with the one she worked on with her sister.
Violet and her mother brainstorm about how the new webzine should look. The following morning, Finch comes to her house and convinces her parents that Violet was only trying to help him, which is why she cut class. Violet’s parents lay down some ground rules about their project so they feel like they are protecting their daughter.
Violet and Finch explore a man’s homemade rollercoasters that afternoon. On the way home, Finch kisses her. The two begin to make out in the back of his car, until he realizes that she is still a virgin. Then the two start using their wandering assignment as an excuse to get together and make out in the back of his car.
On the first warm day of winter, Finch picks Violet up and takes her to the Blue Hole, a bottomless lake. They try, unsuccessfully, to find the bottom together. When Finch tries again, he is under water so long Violet believes he died. When he resurfaces, she is furious. Her anger triggers an outburst that allows her to release some of her guilt and grief about the accident that killed her sister. Finch consoles her. When they stop at his house to clean up after their excursion, they have sex.
Finch starts to drive her home, but they stop to climb the Purina Tower and look out over the town. Unfortunately, they fall asleep, not waking up until the morning. Violet’s parents are furious. They called his mother and learned of Finch’s strange behavior and the lies he has told them about his family. They forbid her to see Finch anymore.
When Finch returns home, he learns that his mother called her ex-husband, Finch’s father, hoping he might know where his son was for the night. Finch’s father arrives and promptly starts to beat on his son but, for once, Finch stands up to him and stops him. Finch’s depression worsens when he cannot convince Violet’s parents to let him see her again.
He moves his comforter into his closet and begins to spend much of his time there. At school, he starts to lose time again. Mr. Embry reveals that he may be bipolar and should talk to a specialist and get medication. All Finch hears is another label to make him more of a freak. When he loses his temper at school, beating up Roamer, he is expelled.
At home, he deletes Mr. Embry’s message from the answering machine so his mother will not hear it and grow worried. Later, he takes a bottle of sleeping pills but runs to the hospital to get his stomach pumped before they can work. He flees the hospital before anyone can find out his identity. He attends a support group for people who have tried or are considering suicide, but it does not help him.
A friend of Violet’s tells her she saw Finch at a suicide prevention meeting. Violet celebrates Finch’s birthday dinner with him in his closet, and she tells him that she knows about his suicide attempt. Finch sends her away. Back home, Violet tells her parents that she has been disobeying them and seeing Finch, but that she loves him, and she needs their help to save him.
They try to call his mother, but leave a message on the machine that, unbeknownst to them, she never checks. When Finch does not show up to school, Violet goes to his house. His sister tells her that he is not home but that they are not worried, as he often disappears for several days at a time.
As days turn into weeks, Violet becomes increasingly worried. Finch finally sends her a cryptic message but turns off his phone before she can call him back. His mother assures her that Finch has promised to call her every Saturday to let her know he is safe and not to worry. But when he misses a call and then sends his family, Violet and his other two friends messages that ring of goodbye, Violet sets out to find him.
She searches his room for clues and figures out where he may have gone from the notes in his closet. She returns to the Blue Hole, the place of their most perfect day together. She finds his clothes, neatly folded on the bank. The police send divers into the water, and they eventually find his body.
As a final goodbye, Finch has left clues for Violet to explore more places in Indiana. At each place, she finds a message of some kind from Finch. They help her to grieve him and let him go, being grateful for the effect he had on her life.