Chapter 1: The narrator, Christopher Boone, introduces himself and explains that he is a 15-year-old boy with Asperger’s syndrome. He discovers his neighbor’s dog, Wellington, dead in the garden and decides to investigate the incident.

Chapter 2: Christopher’s father, Ed Boone, becomes angry when he finds out that Christopher has been investigating Wellington’s death. He tells Christopher to stop and threatens to take away his pet rat, Toby.

Chapter 3: Christopher decides to continue investigating Wellington’s death despite his father’s warning. He interviews his neighbors and learns that Mrs. Shears, Wellington’s owner, had a fight with his father on the night of the incident.

Chapter 4: Christopher’s teacher, Siobhan, encourages him to write a book about his investigation. Christopher begins to write the book and includes diagrams and maps to help him understand the events.

Chapter 5: Christopher visits Mrs. Shears to ask her about the night of Wellington’s death. She becomes upset and tells him to leave.

Chapter 6: Christopher’s father tells him that his mother died of a heart attack two years ago. Christopher becomes upset and decides to run away to London to find his mother’s grave.

Chapter 7: Christopher travels to London and has a difficult time navigating the city. He becomes overwhelmed and scared.

Chapter 8: Christopher finds his mother’s address in his father’s belongings and decides to visit her. He meets his mother’s friend, who tells him that his mother is alive and living in London.

Chapter 9: Christopher’s father comes to London to bring him back home. Christopher refuses to go and decides to stay with his mother.

Chapter 10: Christopher’s mother explains that she left him and his father because she couldn’t handle his behavior. She tells him that she wants to be a part of his life again.

Chapter 11: Christopher’s father comes to London again and apologizes for lying to him about his mother’s death. He tells Christopher that he loves him and wants him to come home.

Chapter 12: Christopher returns home and continues his investigation into Wellington’s death. He discovers that his father killed the dog and becomes upset.

Chapter 13: Christopher runs away again and decides to go to London to live with his mother. He takes Toby with him and leaves a note for his father.

Chapter 14: Christopher arrives in London and reunites with his mother. She tells him that she will take care of him and help him with his condition.

Chapter 15: Christopher’s father comes to London to bring him back home again. Christopher decides to stay with his mother and continue his investigation into Wellington’s death.