Christopher Boone's mother in Mark Haddon's The Curious Incident of the Dog in the Night-Time is absent from her son's life at the outset of the novel. Because Christopher, the idiosyncratic protagonist and narrator, is assumed to be on the autism spectrum, he seldom describes his mother in emotional terms (preferring to describe her as "short"). A hallmark of Christopher's condition is that he prefers to think about and describe his world logically and physically rather than in an emotional way.

Christopher grows up assuming that his mother died of a heart attack. One day, he finds a handful of letters from her addressed to him and dated after her presumed death. Christopher tries to explain this at first by assuming that they had been put into the wrong envelopes. When he realizes the truth, Christopher is angry with his father for concealing her existence.

As Christopher eventually realizes, his mother, Judy, has been living with London with Christopher's former neighbor, Mr. Shears. The letters that Christopher finds eventually reveal his mother to be a caring, if slightly flawed and volatile, individual. In one of her several dozen letters (to which, because they were kept from him, Christopher never responded), Judy recounts an episode in which Christopher had a tantrum in a department store which she could not control, causing her both public embarrassment and private shame at not being an adequate mother. Judy makes many confessions in her letters, including admitting that she is not a competent mother. She also explains that she left because she assumed that Christopher and his father would be better off without her.

Nevertheless, Christopher makes it his mission to navigate public transportation to London in order to find his mother, using the address on the envelopes of her letters. When Christopher arrives in London, though his descriptions are characteristically devoid of emotion, it is clear that, though Judy and Mr. Shears have been cohabiting, their relationship is tumultuous (owing to Judy's proneness to fragility and depression and Mr. Shears's drinking problem). Ultimately, Christopher chooses to stay with his mother, who breaks up with Mr. Shears. Because of Judy's work schedule at a new job, Christopher ends up splitting time with his father and mother. The latter lives in a one-bedroom apartment that requires Christopher to share a bathroom with strangers, which Christopher finds repulsive.

Christopher's preference for his mother as well as her persistence in finding her reveals his concern for her presence in his life, even in the absence of an acknowledged emotional connection. Despite his autistic characteristics, Christopher's actions, if not words, evidence a deep emotional connection with his mother. Likewise, Judy's decision to leave Mr. Shears to be with Christopher demonstrate her dedication to her son, despite the practical and emotional difficulties that his condition poses for her.

In The Curious Incident of the Dog in the Night-Time, how does Haddon develop Christopher's character?

Christopher is the appealing and sympathetic autistic teenager who is the protagonist and tells us the story from his point of view. Because of the first person narrative, it is his character that dominates the novel as we see everything through his eyes. What is stressed throughout the novel is the way that Christopher finds the adult world so hard to comprehend and understand. Note how he links prime numbers and life in the following quote:

Prime numbers are what is left when you have taken all the patterns away. I think prime numbers are like life. They are very logical but you could never work out the rules, even if you spent all your time thinking about them.

Throughout the novel, Haddon creates a contrast between Christopher's character, who, by his own admission, does not "tell lies" and sees everything incredibly literally, and the world of deceit and lies in which adults exist. Christopher as a character strictly doesn't "change," as he remains incapable of lying and unable to understand the interactions of those around him, but the narrative mode creates a juxtaposition between Christopher and the often petty disagreements of adults. The character of Christopher therefore emphasises the way in which adults are often more childish than children themselves, which is a key theme of this novel.