The Curious Incident in the Night-Time was published in 2003 and is Mark Haddon's first novel for adults. It is set in Swindon, a small English town described by one of the characters as "the arsehole of the world".

It is a first person narrative told by fifteen-year old Christopher and the reader quickly becomes aware that Christopher is, in his own words, "someone who has behavioural problems". In an interview the author Mark Haddon states that he regrets that "the phrase ‘Asperger Syndrome’ appeared on the cover of Curious Incident when it was first published". He goes on to explain that his novel is, of course, about "disability and our attitudes towards it, but it's about many other things as well: mathematics, families, Sherlock Holmes, truth, bravery …"

The narrator and main character Christopher is very good at maths but he has a hard time relating to people and finds them and their emotions "confusing", as he says. When Christopher finds a dead dog in his neighbourhood, he decides to "do some detective work" and find out who committed this terribly cruel act. At school, Christopher is asked to write a story, so he decides to write about his investigation and introduces the book as "a murder mystery novel".

In the course of his investigation, Christopher will uncover secrets and realise that the people around him, notably his father, have lied to him. For someone who describes himself as unable to lie, this is difficult and traumatic. When he discovers that his father has lied to him about his mother being dead, Christopher decides to run away to London and find her.

To solve the mystery of the dead dog and the truth about his family, Christopher embarks on a journey of self-discovery. In order to be able to step out of his comfort zone, he keeps reminding himself that he has to be brave. In the end, he knows he can deal with life and whatever happens because "I solved the mystery of Who Killed Wellington? and I found my mother and I was brave and I wrote a book and that means I can do anything".
So, as the author points out, the novel is not merely about a disabled teenager, it is also about family ties and the lies that many families try and hide. Adults all have skeletons in their closets and try and protect other family members, mainly children, from finding out the truth about who they really are. However, as Christopher finds out in his journey of self-discovery, the truth will make you stronger and empower you. So The Curious Incident of the Dog in the Night-time is a coming-of-age novel as well.

Everything that happens in the novel is seen through Christopher's eyes. Mark Haddon's style reflects the narrator's thought process and the unusual way in which he perceives the world. Christopher tells his story in a very matter of fact way. Metaphors are not for him and as he says : "people often talk using metaphors" and he has to decode them. Christopher's "voice" may sound at times childish as illustrated by his many references to "poo". However this means the reader has to fill in the blanks left by Christopher's inability to make sense of what happens at times around him, so as Mark Haddon himself explains "It’s also a novel about the act of reading".