The book opens seven minutes after midnight, when the narrator, Christopher John Francis Boone, finds Wellington, the poodle belonging to Mrs. Shears, his neighbor, dead on Mrs. Shears's lawn with a garden fork through its side. Christopher touches the dog’s muzzle and observes that it is still warm. He wonders who killed Wellington, and why.
Departing from his story (Christopher does this frequently throughout the novel), Christopher explains that he has difficulty determining people’s emotions from their facial expressions. But he can name each country in the world, their capitals, and every prime number up to 7,057. He recalls the first time he met Siobhan, eight years earlier. She drew faces on a piece of paper and asked him what emotions the faces expressed. Christopher could only identify the sad face, which represents how he felt when he found Wellington dead, and the happy face, which shows how he feels when he wanders the neighborhood at three or four in the morning. He could not identify the other emotions.
The story returns to Mrs. Shears’s lawn, where Christopher removes the garden fork and picks up Wellington. Mrs. Shears appears on her patio and yells at Christopher to get away from her dog. Mrs. Shears does not stop, even when he puts the dog down. So Christopher puts his hands over his ears and curls into a ball on the grass, trying to block out the sound.
Christopher reveals that we are reading his murder-mystery novel, written after Siobhan advised him to try writing a story he would want to read. Siobhan thought that the opening of the novel should grab people’s attention, which is one of the reasons that Christopher started it with Wellington's death. The other reason is that he could not start it any other way: this story actually happened to him, and he has trouble putting events in any order other than the order in which they occurred.
At the crime scene, two police officers arrive. Christopher initially finds their presence comforting, but he grows agitated when the policeman begins to ask him questions too quickly, seeming to implicate him in the murder. Christopher curls into a ball again, and he hits the police officer when the officer tries to lift him to his feet.
Christopher states that his book will not be funny. To be funny you have to tell jokes, and jokes often rely on the multiple meanings of words. The fact that one word can have multiple meanings confuses Christopher and makes him uncomfortable, so he will not put jokes in his book.
The officer arrests Christopher for assault. As the officer drives him away, Christopher considers the Milky Way through the window of the squad car. He feels comforted by the order he sees in the stars, and by the fact that policeman has done his job in a predictable manner.
Christopher describes the rules used to determine prime numbers, a potentially infinite number of which exist. He thinks prime numbers act like life: logical, but impossible to fully comprehend. He likes them, so he has ordered the chapters in his book according to prime numbers.
At the police station, Christopher empties his pockets at the front desk, carefully describing every item. When the police put him in his cell, he marvels that the cell is almost a perfect cube. He wonders if Mrs. Shears lied and told the police that he killed Wellington.
Christopher finds people confusing because they often communicate non-verbally through facial expressions. They also use metaphors, which equate one thing with another when neither has any actual relation to the other.
Father arrives at the station and greets Christopher by holding up his hand with his fingers outspread. Christopher does the same, allowing their fingers to touch. Christopher explains that they greet each other this way because he does not like to be hugged. An officer takes Christopher to the investigator, who releases Christopher with a stern warning.
Christopher explains that, in order to form a lie, he would have to pick an event that did not happen to replace the one that did. But he can’t pick any one thing from among the infinite number of things that did not happen, so he does not tell lies. Consequently, everything that he has written in his book is true.
On the drive home, Christopher tries to apologize to his father for making him come to the police station, but his father does not want to talk about it. When they arrive home, Christopher goes to his room. At 2:07 a.m. he goes to the kitchen to get a drink before bed, and notices his father sitting alone in the living room with tears in his eyes. Christopher asks him if he feels sad about Wellington. His father stares at him for a long time before replying that he does.
The book begins unconventionally, starting with Chapter 2 instead of Chapter 1, and rapidly progresses through the prime numbers until we have finished Chapter 41 at the end of the section. Christopher has chosen to write the book this way simply because he prefers prime numbers, with their specificity of pattern, to standard numbers. Christopher also digresses repeatedly from the mystery of Wellington’s murder right from the start, veering into discussions of what he knows (countries and their capitals, for example) and the difficulties he has understanding people. The reader can see by this point that, although The Curious Incident of the Dog in the Night-time may use some conventions of murder-mystery narratives, it will hardly be a conventional story for that genre. The ways it diverges from convention, digressing into discussions of numbers for instance, give the reader insight into how Christopher views the world. Specifically, Christopher’s observations on prime numbers tell us that Christopher values order and has a gifted mathematical mind.
Christopher has very poor social skills, stemming from his inability to imagine what other people are thinking or feeling, and in this section we already see this limitation playing out in the story. For instance, we see that Christopher is easily misled by lies when Christopher finds his father alone in the living room crying. Father says he feels sad because of Wellington, though the reader recognizes that this excuse is not true. Christopher, who cannot understand that his father is lying, believes him and returns to his room without questioning the matter any further. This difficulty identifying lies makes it all the more extraordinary that Christopher investigates the mystery of Wellington’s murder. We also see Christopher’s poor social skills at work when he has difficulty explaining himself after Mrs. Shears and the policeman confront him about Wellington. He quickly feels overwhelmed and withdraws into a ball. Repeatedly, Christopher’s social deficits lead to misunderstandings and conflicts. For instance, Christopher’s inability to explain why he was holding Wellington’s body leads Mrs. Shears to think that Christopher killed Wellington. In fact, Christopher’s poor social skills play such a prominent role right from the start of the story that the reader can assume they will have greater ramifications later on.
Christopher recognizes his social limitations, and he focuses instead on the extraordinary intelligence he displays in other regards. The main evidence of this intelligence comes from Christopher’s ability to deal with concepts that other people might find abstract and difficult to comprehend. He clearly and succinctly explains why the Milky Way appears in the sky as it does, for example. He also tells the reader that he can identify all the prime numbers up to 7,057, indicating that he has a particularly savantlike ability with numbers. Christopher compares prime numbers to life, saying that both are logical but you could never work out the rules no matter how hard you try. He believes that, like prime numbers, life abides by rules. In other words, he does not see life as random and chaotic, even though he recognizes that he cannot know all its rules. Instead, Christopher knows his strengths and weaknesses and lives contentedly with them.
Christopher’s obsession with the physical details of his surroundings, particularly aspects of color, number, and time, serves as a great asset to him in his investigation. Christopher describes scenes in very specific detail. After the police put him in jail, for instance, he comments on the ordered dimensions of his cell before considering why he is in prison in the first place. When the officer makes him turn in his belongings at the police station, he lists in great detail every item in his pockets. This attention to detail helps Christopher to counter the disadvantages he faces from his lacking social skills and allows him to gather clues related to Wellington’s murder. He notices that Wellington’s muzzle still feels warm when he finds Wellington dead, for instance.