The Artemis Fowl series is about a teenage former sociopathic genius criminal and an Elven hot-shot, loose-cannon cop. They fight crime. No, really.
What began as a deep rivalry between the titular criminal and his fairy enemy Holly Short (and their various companions) has, over the course of six books, morphed into a friendship. With the main hostility gone, it’s felt increasingly like author Eoin Colfer has been reaching for things to do. This time it’s that old fantasy favorite: Time Travel.