Christopher Boone finds his neighbor's dog dead in her front yard with a pitchfork sticking out of it in the nighttime. He wonders who killed it, and ultimately decides to write a murder/mystery book where he tries to figure it out.

However, there is a catch. Christopher has a disability that has been compared with an autism spectrum disorder called Asperger syndrome. This disorder makes it difficult for him to understand certain social situations like body language. His disorder doesn’t affect certain parts of his brain so he’s really good at math and memorization.

When Mrs. Shears, Christopher's neighbor, finds him with her dead dog, she calls the police. As a result, Christopher has to spend a few hours in a jail cell and interrogation. When his father comes to get him, he tells Christopher not to investigate the dog's death anymore. Christopher thinks of ways to still do all of his detective work while not disobeying his father.

Christopher starts asking neighbors to see if anyone knows anything about the dog's death. His first lead is Mr. Shears since he left his wife two years ago and could possibly hate her. He promises he'll stop investigating when Christopher's father finds out he's been asking people about the dog.

This book is a fast-read about a persistent boy figuring out secrets about his family.