Half Moon Investigations by Eoin Colfer

Moon Fletcher is a twelve-year old boy who likes to "play detective". He was solving a case. One day, someone hits him in the face with a metal object. He loses his senses. The next morning his parents found him and brought him to the hospital. When he woke up, he escapes from the hospital. Someone was trying to accuse him of something he dadn't done, and he was going to find out who this person was. Moon decides to go temporaneily to live with Red's family. Moon was suspecting that Red was the person who had tried to square him. Moon sees the metal object. He runs out of that house, and goes to the police to tell what had really happened. Moon had solved the biggest mystery of his life, and got the biggest criminal of his town arrested.