John Green's sixth novel The Fault in Our Stars is a sad, funny, hopeful, and charming love story between two teenagers who have been diagnosed with terminal cancer. Hazel Lancaster is 16 years old with thyroid cancer and Augustus Waters is 17 years old who has osteosarcoma. When the novel begins Hazel's mother forces Hazel to go to Support Group because she's worried her daughter is suffering from depression. Hazel wears a cannula and carries around an oxygen tank she calls Phillip to support her weak lungs. Hazel comments that depression is a side effect of dying. She reluctantly goes to Support Group after she gets to record the next episodes of an America's Next Top Model marathon. When Hazel arrives at the church where the Support Group for cancer-stricken youth gather she is immediately annoyed by the leader Paul who always opens a meeting with his testimony about surviving testicular cancer. She sighs with her friend Isaac about the routine of the meetings.
Hazel does not expect to meet anyone new and is surprised to see a good-looking boy staring at her. After he keeps staring at her for awhile she stares back at him and he finally looks away. The cute boy introduces himself as Augustus Waters and says he's been cancer free for over a year after a battle with osteosarcoma that led to his right leg being amputated. He tells the group that he fears oblivion and a normally reticent Hazel speaks up saying "There was time before organisms experienced consciousness, and there will be time after. And if the inevitability of human oblivion worries you, I encourage you to ignore it. God knows that’s what everyone else does.” Augustus is impressed and smiles brightly at Hazel. Isaac talks about his upcoming surgery that will remove his remaining eye due to a rare care. When Support Group ends Hazel and Augustus observe Isaac and his girlfriend Monica making out. Hazel feels charmed by Augustus until he pulls a cigarette out. She gets angry, but he explains “It's a metaphor, see: You put the killing thing right between your teeth, but you don't give it the power to do its killing.” Hazel accepts his offer to see V for Vendetta at his house. Hazel meets Gus's parents and they watch the movie. Hazel tells Gus about her favorite book An Imperial Affliction and he gives her his favorite book The Price of Dawn. He wants to see her again, but she says she'll call him after she finishes reading his book. Hazel likes him, but she's scared that she's going to hurt him. Augustus reads An Imperial Affliction and is completely frustrated with its ending or lack thereof. Hazel explains that she's been trying to contact the author Peter Van Houten for years and never got a response. After Isaac gets his eye surgery he is extremely distraught over his girlfriend dumping him when Hazel visits him in the hospital and even when he's released. Augustus reveals that he's been able to correspond with the elusive Peter Van Houten through his assistant Lidewij Vliegenthart. As the days pass Hazel finds herself falling in love with Augustus despite feeling like a "grenade." These worries lead her to briefly obsess over Gus's last girlfriend who died from a brain tumor.
Hazel has an emergency medical trip and stays in the Intensive Care Unit for several days. She keeps her distance physically and tells Gus they can't kiss. During a meticulously planned picnic Augustus takes Hazel to a museum park and announces that he's been granted his wish from the Genies to take them to Amsterdam to meet Van Houten. Despite initial pushback from Hazel's doctors, the trip gets approved. When Hazel and her mother arrive to pick up Gus they hear him sobbing and screaming to his parents that it's his life and he can do what he wants. On their plane ride to Amsterdam Gus confesses his love for Hazel with a grand speech: "I'm in love with you, and I'm not in the business of denying myself the simple pleasure of saying true things. I'm in love with you, and I know that love is just a shout into the void, and that oblivion is inevitable, and that we're all doomed and that there will come a day when all our labor has been returned to dust, and I know the sun will swallow the only earth we'll ever have, and I am in love with you.” In Amsterdam Hazel and Gus are treated to a fancy dinner facing the canal by Van Houten. They drink champagne and eat the best food they've ever had. The next day they go to visit Peter Van Houten. He is surprised by their appearance and yells at his assistant to get rid of them. Lidewij invites them in and they learn that Van Houten never wanted them to come and that he's a raging alcoholic. He says cruel things about Hazel's cancer and doesn't answer any of her questions about his book despite Hazel shouting at him. Gus takes Hazel's hand and they leave abruptly. Lidewij quits her job and runs after them. She tells them she's sorry about his behavior and that she arranged the whole visit hoping that it would help Van Houten come out of his drunken stupor. Lidewij takes them to the Anne Frank House. Hazel and Gus passionately kiss when they get to the top floor. They go back to Gus's hotel room and make love for the first time. They spend the next day together sight-seeing, but before they leave Hazel's mother tells Gus they need time to talk. Gus then confesses to Hazel that while she was in the ICU he got a PET scan and his cancer recurred nearly everywhere in his body.
Hazel spends every day with Gus as his body deteriorates. Gus's charming personality is badly affected after a hospital stay where he has to start using a wheelchair. In the middle of one night he calls her and tells her he is at a gas station and can't reinsert his G-tube. Hazel sneaks out and meets him. He vomits and starts sobbing and saying he hates himself and his life. She holds his face and comforts him by mentioning the movie they watched together on their plane ride to Amsterdam. A few days later Gus calls Hazel for an emergency Support Group session and tells her to write a eulogy for him. Hazel's mom and dad want her to stay home because she's spent too much time with Gus lately. She yells that Gus asked her to write him a eulogy and that she would be home every day very soon. At the Support Group only Gus and Isaac are there. Isaac reads his eulogy for Gus and pokes fun at his conceited and talkative nature, then closes with "When the scientists of the future show up at my house with robot eyes and they tell me to try them on, I will tell the scientists to screw off, because I do not want to see a world without him." Hazel goes up and reads her eulogy. She tries her best to maintain her composure as she reads about their love story: "I can't talk about our love story, so I will talk about math. I am not a mathematician, but I know this: There are infinite numbers between 0 and 1. There's .1 and .12 and .112 and infinite collection of others. Of course, there is a Bigger infinite set of numbers between 0 and 2, or between 0 and a million. Some infinities are bigger than other infinities. A writer we used to like taught us that. There are days, many of them, when I resent the size of my unbounded set. I want more numbers than I'm likely to get, and God, I want more numbers for Augustus Waters than he got. But, Gus, my love, I cannot tell you how thankful I am for our little infinity. I wouldn't trade it for the world. You gave me a forever within the numbered days, and I'm grateful.”
Augustus dies in the hospital eight days after his pre-funeral. At his real funeral Hazel puts a pack of cigarettes in his casket and kisses him on the cheek. She is shocked to see Van Houten has attended. He tells her that Gus corresponded with him after their trip and told him the only way he'd make up for ruining their visit is by attending his funeral and writing a eulogy for Hazel. At this point Hazel is over Van Houten and calls him a pathetic drunk after Gus's funeral. A week later Hazel goes to Isaac's house and they play a video game that Gus loved. Isaac mentions that Gus was writing something for Hazel, an epilogue to the book she liked. Hazel frantically tries to find out where Gus may have left his writing and visits his house to search his bedroom. She finds nothing, but after a conversation with her friend Kaitlyn she realizes he must have sent it to Van Houten. She contacts Lidewij who returns to Van Houten's place with her boyfriend to retrieve Gus's last letter. She scans the letter and emails it to Hazel, telling her she is mailing it out. Hazel reads the letter where Gus asks Van Houten to add to his eulogy for Hazel or edit it. The letter closes with Gus affirming his love for Hazel and not regretting their time together: “What else? She is so beautiful. You don’t get tired of looking at her. You never worry if she is smarter than you: You know she is. She is funny without ever being mean. I love her. I am so lucky to love her, Van Houten. You don’t get to choose if you get hurt in this world, old man, but you do have some say in who hurts you. I like my choices. I hope she likes hers." Hazel tells Augustus that she likes her choices too.