The Curious Incident of the Dog in the Night-Time. That's quite a hefty title. Let's take a closer look.
Christopher really likes Sherlock Holmes, and he constructs his own book as a murder mystery along the lines of one of Sir Arthur Conan Doyle's stories. As such, he chooses a title similar to Doyle's own, like "The Adventure of the Empty House," or The Hound of the Baskervilles, which Christopher describes at length.
One crucial difference between Christopher's title and Doyle's is that, as his teacher Siobhan notes (7.7), most murder mysteries are concerned with a person's murder, not the murder of a dog. But Christopher argues that the murder of a dog is just as interesting as the murder of a person. Throughout the story, Christopher seems to be able to connect to animals better than he connects to humans, so we see where he's coming from.
We might also point out that in the book's first paragraph, all the elements of the title are introduced and explained: it's shortly after midnight, there's a dead dog lying on the lawn, and the narrator is unsure how and why it came to be there, and why it's dead. The title, perfectly matter-of-fact, is a nice encapsulation of Christopher's "Writing Style."