Christopher John Francis Boone is a fifteen-year-old boy who has behavioural problems, who lives with his father, Ed. He explains in his narration that his mother, Judy, died two years ago. Then one day, the boy discovers the dead body of the neighbour's dog, Wellington, speared by a garden fork. Mrs.Shears, the dog's owner, calls the police, and Christopher comes under suspicion. He is arrested, then released with a police caution. He decides to investigate the dog's death. Throughout his adventures, Christopher records his experiences in a book. During his investigation, Christopher meets the elderly Mrs.Alexander, who informs Christopher that his mother had an affair with Mr.Shears.