Hazel Grace Lancaster met Agustus Waters on a Cancer Support Group meeting. They became friends, and soon enough fell inlove with each other. Together, they went to Amsterdam to talk to Hazel’s favorite author, Peter. about how the book he wrote ended.
Instead of getting an answer, they ended up spending 3 days in Amsterdam hanging with each other because it turns out Peter was an alcoholic man who couldn’t talk anything with sense. On the trip, Gus told Hazel the truth, that he’s dying (although both of them are). Gus wasn’t as healthy anymore, so he died before Hazel did. He let her write an eulogy for him and sent a letter to Peter before dying because the truth was Peter’s daughter died from cancer, the reason why he was that way. Peter wasn’t a mad man after all, he was just depressed.