The Apprentice's Incubus

Used to life on the street, Finn never expected to be hired by a magician after saving him from a rival street gang-let alone a magician with a penchant for book hoarding and performing occasionally-exploding experiments. But Master Kestrall is a kind-hearted man, even if he sends Finn on far too many errands to the bookstore. After all, Finn is infatuated with Jonti, the master bookkeeper's handsome apprentice.
The only problem is, Finn has absolutely no experience in matters of the body and no idea how to go about acting upon his feelings. That all changes when, on one of his regular trips to the Crow's Nest, Finn brings home a certain book that holds some very rare knowledge indeed-and when Finn accidentally-on-purpose summons an incubus into his midst, nothing will ever be the same again.