There's definitely a reason that the book has the alternate UK title of Severed Heads, Broken Hearts...
The Beginning of Everything really does start off with a decapitation at Disneyland. Ezra Faulkner goes to Disneyland with his best friend Toby Ellicott, Toby's mother's attempt at rocketing her misfit son into middle school popularity by sending a group of his "friends" there for his birthday party. When they get there, they go on the Thunder Mountain Railroad, a runaway-train-style roller coaster. Toby and Ezra sit in the back of the car, while the rest of the group sits in the front, and so when a 14-year-old boy from Japan stands up in his seat just before the train careens through a "low-ceilinged tunnel" and he is instantly decapitated, it affects Toby and Ezra differently than their other friends,
What the news reports didn't say was how the kid's head sailed backward in its mouse-ear hat like some sort of grotesque helicopter, and how Toby Ellicott, on his twelfth birthday, caught the severed head and held on to it in shock for the duration of the ride. (3)
Ezra's point in rehashing this story is that he believes that everyone has a moment in his/her life that changes everything. A personal tragedy, and after which, everything that is going to happen is going to happen. Disneyland was Toby's tragedy - after it happened, he became an outcast; Ezra became popular and the two drifted apart. But The Beginning of Everything focuses on Toby's tragedy. After catching his girlfriend cheating on him at a party in his junior year of high school, Ezra leaves abruptly and is hit by a car that has blasted through a stop sign. He ends up in the hospital, his knee completely shattered, necessitating his use of a cane throughout his senior year at high school. Most importantly, the accident destroys his tennis career: its the reason he's popular at high school, the reason he has the friends that he does, and the way he's convinced he'll get into a good college. His life is changed utterly, and he starts his last year of school in a very different place from where he ended his junior year. The accident, he's convinced, is his personal tragedy.
What it does, however, is unwittingly bring him and Toby back together as friends. He ends up joining the debate team, the one that Toby heads, and joining Toby's group of friends at lunch instead of sitting with his own - athletes, jocks, and the popular girls (including his ex-girlfriend). And in joining the debate team, he meets Cassidy Thorpe, a new girl at school who has an unclear past. Cassidy used to debate, although she insists she won't do it anymore. Instead, she wants to help Ezra get better at it, and so the two become friends as Cassidy tries to teach Toby just how, exactly, to drop in quotations from canonical novels and poetry into his debates:
"There's this poem," Cassidy finally said, "by Mary Oliver. And I used to write a line from it in all of my school notebooks to remind myself that I didn't have to be embarrassed of the past and afraid of the future. And it helped. So I'm giving it to you. The line is, 'Tell me, what is it you plan to do/With your one wild and precious life?'" (114)
Ezra finds out who he is in the aftermath of his own personal tragedy, and begins to navigate the space between his past and future - two very different sides of a coin. He goes on overnight debate trips; flashes Morse code out his window to Cassidy, who lives across the park; avoids his ex-girlfriend; and ultimately learns what it means to recover and move on. As Ezra describes near the end of the book, "I wondered what things became when you no longer needed them, and I wondered what the future would hold once we'd gotten past our personal tragedies and proven them ultimately survivable" (333). There's no question of why this book was considered a "best of 2013" on so many lists. An interesting and surprising premise (I can't think of any book ever that has started out with a Disneyland decapitation) evolves into the meaning of tragedy, change, and moving on, as Ezra Faulkner leads readers through his truly transformative senior year of high school.