The Curious Incident of the Dog in the Night-time takes place in the year 1998 in and around the town of Swindon, England. The fifteen-year-old narrator of the story, Christopher John Francis Boone, discovers the slain body of his neighbor’s poodle, Wellington, on the neighbor’s front lawn one evening and sets out to uncover the murderer. His investigation is at times aided, and at other times hampered, by the mild form of autism he lives with. After Christopher hits a policeman in a misunderstanding at the scene of the crime, the police take Christopher into custody. They release Christopher with only a stern warning, under the condition that he promises to them and to his father not to look into the murder any further.
Christopher chronicles his investigation in a book—the book we are reading—as part of a school assignment. Ignoring repeated warnings from his father, Christopher investigates the crime scene and conducts interviews with the residents of his block. He uncovers a more tangled plot than was first apparent when he discovers that his father and the owner of the slain dog, Mrs. Shears, had a romantic affair. He subsequently learns that their affair began in reaction to another relationship, one carried on between Mr. Shears and Christopher’s mother, before she disappeared from Christopher’s life.
At school, Christopher prepares for an A-level math exam that will enable him to attend a university, a feat no other child at his school has managed. He also continues to work on his book. Upon returning home one afternoon, Christopher accidentally leaves his book in plain view on the kitchen table. His father reads it, becomes angry, and confiscates it. Later, Christopher searches for the book and uncovers a series of letters, hidden in a shirt box in his father’s closet, addressed to him from his supposedly dead mother. The letters chronicle a life that his mother has continued to lead with Mr. Shears in London and contain repeated requests for Christopher to respond. In shock, Christopher passes out in his bedroom surrounded by the evidence of his father’s deception. When Father comes home and realizes what has happened, he breaks down in tears. He apologizes for his lies, explaining that he acted out of a desire to protect Christopher from the knowledge of his mother’s abandonment of the family. Christopher’s father also admits to killing Wellington after an argument with Mrs. Shears, his lover.
Christopher, now terrified of his father and feeling he can no longer trust him, sneaks out of the house and travels to London to live with his mother. During a harrowing journey, he copes with and overcomes the social fears and limitations of his condition, dodges police, and almost gets hit by a train. His arrival at his mother’s flat comes as a total surprise to her, as she had no idea that Christopher’s father had been withholding her letters. Christopher settles in for a time at his mother and Mr. Shears’s flat, but friction caused by his presence shortly results in his mother’s decision to leave Mr. Shears to return to Swindon. Christopher moves into a new apartment with his mother and begins to receive regular visits from his father. When Christopher’s pet rat Toby dies, Christopher’s father gives Christopher a puppy. At school, Christopher sits for his A-level math exam and receives an A grade, the best possible score. The novel ends with Christopher planning to take more A-level exams in physics and further math, and then attend a university in another town. He knows that he can do all of this because he solved the mystery of Wellington’s murder, was brave enough to find his mother, and wrote the book that we have read.