"Half-Moon Investigations" is a 2006 young adult novel by Eion Colfer, probably best known for the Artemis Fowl series. Unlike his other works, it contains no fantasy or science-fiction elements, instead taking place in contemporary Ireland. Although the book is not fantasy, it is somewhat fantastical, containing many episodes that are far-fetched.

The story centers around Fletcher Moon, a 12 year old student in southeastern Ireland with a badge and licence from an online school in private investigation. There is a limited market for his talents in the Irish equivalent of middle school, but the book starts with him taking a case that will change his life. As with many detective stories, the book starts with a minor case that unmasks a larger and larger conspiracy, as well as challenging Moon's notions about the world. Two of his early antagonists are April Devereaux, a well-to-do and socially skilled girl who seems to be superficial, and Red Sharkey, the tough scion of a family of petty criminals. Over the course of the book, Moon learns that neither of these people is who he thought they were. The book's plot has many twists and turns, and some silly episodes, but it is still written with more surprises than many "adult" mysteries. I especially was thrown off by the book's double climax, where the mystery is seemingly solved almost 100 pages before the book's true conclusion.

I also liked that the book's plot allowed the characters to develop. At the start of the book, despite his precocity, Fletcher Moon is still a child, and hasn't looked very deeply at the people around him. At the start of the book, the attitudes, dialog and humor all seem to be at the middle school level. By the end of the book, there has been some actual character development, and the characters, as well as the audience, have been given a wider view of the world. This is another fun, readable and creative book by Eoin Colfer, and I would recommend it for both young adult and adult readers.