Because an adult familiar with Hazel's illness needs to go with her and Augustus to Amsterdam, it's decided that Hazel's mother will go. As Hazel thinks of the trip, she questions why she tensed up when Augustus touched her cheek at the sculpture park. She realizes that, although she finds Augustus attractive, she has never before considered kissing him. Following another one-sided conversation with Kaitlyn, largely about Augustus, Hazel decides to look up Augustus’s late girlfriend Caroline Mather’s profile online. She thinks she and the healthy Caroline looked nothing alike, but cancer made them extremely similar.
Hazel's parents call her down to dinner. She's being very sarcastic and cold as they talk, and when her mother asks what's wrong, Hazel says she's a “grenade.” At some point, she's going to explode and injure everyone near her. She goes to her room to read and can hear her parents talking about her. She understands suddenly that she tensed up with Augustus because she knows being with him will eventually hurt him. She texts him to tell him that she can't kiss him because it makes her think of the pain she'll cause him. He replies that he understands but also flirts with her, to which she simply responds “Sorry.” Eventually her mother enters her room and tells her she's not a grenade to them. She brings them much more joy than sorrow. Just after four in the morning, Hazel wakes up with a terrible pain in her head.
Hazel screams frantically to wake her parents. She feels what seems like a series of explosions in her head. The feeling is so awful that for a brief moment Hazel waits for her death, which doesn't come. She equates the sensation to being on a seashore with waves crashing over her, while not being quite allowed to drown. The next thing we know Hazel wakes up in the ICU. Her father explains that the headache was brought on by poor oxygenation, which resulted from her lungs filling with fluid. Hazel’s father also explains that Dr. Maria remains very optimistic, having run a total body PET scan and finding no new tumors. At this point Hazel’s nurse kindly ushers her father out of the room, citing Hazel’s need for rest. While feeding Hazel ice chips, the nurse mentions that Hazel has been out for a few days, that the world has not much changed, and that Augustus has been outside in the waiting room ever since her arrival, though he has been prohibited from seeing her directly.
On Hazel’s last day at the hospital, Augustus is briefly allowed to visit, whereupon he delivers another correspondence from Van Houten. The letter speaks of the hamartia, or fatal flaw, evident in Hazel's and Augustus’s situation. He goes on to say Shakespeare was wrong when he had Cassius note that “The fault, dear Brutus, is not in our stars / But in ourselves.” He also cites Shakespeare’s fifty-fifth sonnet, calls time a slut because she “screws everybody,” and lastly defends the logic of Hazel’s decision to minimize the pain she inflicts upon others. By the time Hazel finishes Van Houten’s letter she is already wondering if Dr. Maria might clear her for international travel.
A main focus of this section is Hazel's struggle to come to terms with the knowledge that being close to people will cause them a great deal of pain when she dies. One of the very harsh realities Hazel faces is that she will ultimately die of her cancer and that those close to her will have to deal with the emotional trauma of her death. Looking at Caroline Mathers's online profile and the comments left for her makes this reality suddenly more immediate, and Hazel begins describing herself as a “grenade” that will inevitably blow up and hurt everyone close to her. She finds herself in a paradox: She wants to be close to her parents and Augustus, but she doesn't want to hurt them, and she thinks being close to them will do just that. Her reaction is to push them away in order to keep them safe. She realizes that's why she tensed up when Augustus touched her at the sculpture park: She was afraid of him kissing her, which would bring them closer. She even goes a step further by texting him to tell him they can never kiss. She also has an angry emotional outburst at the dinner table, which is a way of creating opposition, and therefore emotional space, between herself and her parents. (Notably, in the game he played with Isaac earlier Augustus threw himself on a grenade in a heroic sacrifice, or at least a simulated one. With the grenade symbolism this section establishes, that act suggests there's something heroic in being willing to get close to someone and get hurt for the right cause.)
In these chapters we see why the title of the novel, which appears here in Van Houten's letter to Augustus, is relevant to Hazel and Augustus, and it ties into the motif of existentialism. In the quote from Shakespeare's play “The Tragedy of Julius Caesar” that the title of the book comes from, the “stars” Cassius refers to represent fate. Basically Cassius tells Brutus that they can't blame their situations on fate, but rather that they're the ones responsible for their circumstances. Van Houten points out that, for Hazel and Augustus, this point of view couldn't be more wrong. Hazel and Augustus are not to blame for their cancers or the complications their illnesses cause. Instead they find themselves struggling to navigate a situation that has no apparent meaning—their cancers aren't obviously a punishment for any past actions, for example—and is beyond their control to change. The apparent lack of meaning of many of life's events and our inability to control them are central preoccupations of existentialism. Here, of course, they play out through the characters of Hazel and Augustus, who despite being just teenagers have to contend with serious questions about meaning and purpose.