Did Somebody Just Explain Magic in a Way That Actually Made Sense?

A lot of fantasy and horror tales contain magic, or at least supernatural creatures, and never explain how they got there. But once in a while, we get an explanation for how magic entered our rational world — and it just works. What's your favorite example of a story that actually explains magic well?

Illustration of a scene from Perdito Street Station, by Fred Gambino

Pick a movie, book, comic, TV series or game — up to you! Just tell us how what the explanation was and why it worked. Also, please include pictures, links or clips! That makes it so much better.