From the first day that Hazel meets Augustus, the two are practically inseparable. The basis of their relationship ends up being Hazel's favorite book, An Imperial Affliction. She requires Augustus to read it and in turn, he requires her to read the book that is the basis of his favorite video game. Hazel relates to the character in her favorite book, Anna, because Anna has a rare blood cancer. Augustus and Hazel bond over the book because both of them of a burning desire to find out how the story ends because the author stops the book before providing conclusion on what happens to each of the characters.
Augustus joins Hazel's pursuit of the book's author, Peter Van Houten, to provide the answers that they need. Augustus even uses a wish foundation to fly him and Hazel to Amsterdam, where the author lives, to talk with him in person. While Hazel is the one that is doomed to die, Augustus ends up telling Hazel that at his recent scan, the doctors discovered that his entire body is filled with cancer. Hazel spends the last months of Augustus's life caring for him and loving him.