Clay Jensen is a diligent high school student. He is close to being class valedictorian and almost always chooses to study on weekends instead of going to parties. Clay’s classmate, Hannah Baker, has recently taken her own life. After Hannah’s suicide, Clay receives a package in the mail with no return address. When he opens it, he a shoebox containing seven two-sided audio cassettes with the A and B sides numbered in sequential order.

We learn that the tapes were recorded by Hannah just prior taking her own life, and that on thirteen of the fourteen sides she described troubling events leading up to her suicide. Thirteen Reasons Why follows Clay as he travels around town, with the aid of a map that Hannah created, listening to Hannah’s voiceover as she describes the events (one per tape side) and the key individuals involved in them—all of whom Hannah holds culpable in some way for her decision to take her own life. Clay, who was not close friends with Hannah, is initially puzzled about why he was sent the tapes, but as he listens to more and more of her disturbing stories, he belatedly begins to understand that he had an important place in Hannah’s world and psyche. 

Clay listens to the first tape on an old stereo his family’s garage. He hears Hannah say that she will explain why she took her own life, but that anyone listening to the tapes is one of the reasons she did so. Hannah says that whoever receives the tapes should listen to them and then send them on to the next person listed. She warns that if anyone either tries to avoid listening to the tapes or doesn’t pass them on, a backup set of the tapes will be released. In addition to the tapes, each recipient has received a map with different places marked, so that they can travel around town to each location mentioned in Hannah’s story.

On Cassette 1, Side A, Hannah tells of dating Justin Foley, who was her first kiss. They dated for a month, but when rumors started to circulate (some of them originating with Justin), Hannah gained a reputation for being promiscuous. Hannah addresses this on the tape with the statement, “Hannah Baker is not, and never was, a slut.” Realizing he’ll need way to listen to the rest of the tapes as he travels around town, Clay goes to his friend Tony’s house to get a Walkman. 

After leaving Tony’s, Clay listens to Cassette 1, Side B. On it, Hannah discusses Alex Standall. Hannah, Alex and a girl named Jessica Davis became friends and started spending time at Monet’s, a local coffee shop. After Jessica and Alex had an unpleasant breakup, Alex made a “Who’s Hot / Who’s Not” list and passed it around school. Trying to make Jessica angry, Alex listed Hannah as “Best Ass in the Freshman Class” and listed Jessica as the worst. Shortly afterwards, a student came up behind Hannah and spanked as she was standing in line at a store. With the promiscuity rumors already circulating, Hannah believes that Alex’s list gave the student an excuse for his behavior.

Clay sits on the curb outside the store where the incident occurred and plays the next tape, Cassette 2, Side A. Hannah describes her friendship with Jessica Davis. After the “Who’s Hot / Who’s Not” list started to circulate through school, Jessica confronted Hannah, stating that the promiscuity rumors must be true, and that Hannah had been involved with Alex. Hannah tried to explain that Alex put their names on his list just to make Jessica jealous, but Jessica became angry and struck Hannah, leaving a small scar above her eyebrow. Clay takes a city bus to Monet’s and orders a coffee.

At Monet’s, Clay listens to Cassette 2, Side B. Hannah talks about a yearbook photographer, Tyler Down, who secretly took pictures of her from outside her bedroom window. Hannah asked a fellow classmate, Courtney Crimsen, to help her catch this Peeping Tom in the act. In Hannah’s room, she and Courtney talk loudly and provocatively to entice the photographer, and then run to the window and see someone who Hannah later confirms is Tyler. Hannah has recorded this tape while standing outside Tyler’s window, and she marks his address on the map so others can invade his privacy, just like he invaded hers.

While taking another bus to get to Tyler’s house, Clay sees that a fellow student, Skye Miller, is also aboard. He had a crush on her in eighth grade, but Clay says that at some point Skye stopped talking to other students. Exiting the bus, Clay sees that Tyler’s window has been broken. On Cassette 3, Side A, Hannah talks about Courtney Crimsen, who everyone assumes is a good person. Hannah gives examples of how Courtney manipulates people and is quite fake. After giving Courtney a ride to a party, she even tried to start new rumors about Hannah.

On Cassette 3, Side B, Hannah describes going on a date with Marcus Cooley at Rosie’s, a local diner. While sitting in a booth, Marcus put his hand on Hannah’s thigh. After he refused to remove his hand, Hannah shoved him out of the booth. He loudly called her a “tease” and left. 

Clay thinks about how he and Hannah used to work at the local movie theater together. He had feelings for her but couldn’t bring himself to tell her because he was worried what people would think about him given Hannah’s reputation. 

Clay walks to Rosie’s Diner. On Cassette 4, Side A, Hannah tells how Zach Dempsey interfered with her life. In Mrs. Baker’s Peer Communications class, each student had a paper bag in which other students could leave anonymous compliments. After realizing that she was no longer receiving compliments, Hannah caught Zach stealing them. Hannah understood that Zach’s actions were childish, but says that this was a time in her life when she needed encouragement. Hannah then left a note in Mrs. Baker’s paper bag requesting a class discussion topic. On the note, Hannah said that she was contemplating suicide. Hannah was hurt when many students voiced annoyance over the topic and the anonymous student who’d suggested it.

Still at Rosie’s, Clay listens to Cassette 4, Side B. Hannah talks about Ryan Shaver, the editor of a school publication called the Lost-N-Found Gazette. She and Ryan met at a poetry group and got along. Ryan published one of Hannah’s poems in the Lost-N-Found Gazette without her permission. While he did not put her name on it, some students guessed who wrote it and made fun of her. Hannah felt as though her thoughts and feelings were offered up for ridicule.

When Clay leaves the diner, Tony is waiting and tells Clay to get in his car. Tony explains that he has the second set of tapes and that he’s been making sure that everyone on the list listens to them and passes them on. 

Clay listens to Cassette 5, Side A—the tape about him. Hannah talks about the time she and Clay connected at a party, eventually kissing in an unoccupied bedroom. But Hannah, exhausted from the stress of her life, freaked out and told Clay to leave, which he did.

Tony drives through different neighborhoods while Clay listens to Cassette 5, Side B. Hannah continues her story of the party, from the moment after Clay left. While hiding in a closet, she heard Bryce Walker sexually assault Jessica Davis, who was passed out on the nearby bed. The tape is actually dedicated to Justin Foley, though, because he left Jessica in the room and let Bryce in, knowing what Bryce would do.

Disgusted by what he’s heard, Clay leaves Tony’s car and starts walking. On Cassette 6, Side A, Hannah tells of leaving the party where the assault occurred with Jenny Kurtz. While driving Hannah home, Jenny ran over a stop sign. Hannah thought that they should tell the police, but Jenny didn’t want to get in trouble, so she drove off, leaving Hannah to walk home. Later that night, there was an accident at that intersection in which a student from Hannah and Clay’s school was killed. 

Clay listens to Cassette 6, Side B, in which Hannah tells a story about giving up on herself. Late at night, Hannah walked past a house where a party was winding down. Bryce Walker asked Hannah to join him in a hot tub. Hannah knew that it was a terrible idea but stripped down to her underwear and got in anyway. Bryce put his hands in Hannah’s underwear, despite Hannah turning away from him and crying. On the tape, she states that she never told him “no,” and that she was just using him to let go of life completely. 

On Cassette 7, Side A, Clay listens to a conversation that Hannah had recorded between herself and her school guidance counselor, Mr. Porter. She tells Mr. Porter that she is considering suicide, and he tries to help her, but the conversation only angers Hannah. When she leaves his office, he doesn’t pursue her. 

The next morning, Clay mails the tapes to Jenny Kurtz, who is next on the list. When he goes to school, he sees Skye Miller, the girl from the bus who stopped talking to other people. Clay runs after her and talks to her.