Every Inch a King — Harry Turtledove

Otto of Schlepsig is risking his neck as an acrobat in a third-rate circus in the middle of nowhere when news arrives that the land of Shqiperi has invited Prince Halim Eddin to become its new king. Otto doesn't know the prince from Adam, but he does happen to look just like him -- a coincidence that inspires Otto with a mad plan to assume Halim's identity and rule in his stead. True, Shqiperi is an uncivilized backwater, but even in uncivilized backwaters kings live better than acrobats. Plus, kingship in Shqiperi comes with a harem. Rank, as they say, has its privileges.

With his friend Max, a sword-swallowing giant whose chronic cough makes every performance a potential tonsillectomy, Otto embarks on a rollicking journey filled with feats of derring-do, wondrous magic, and beautiful maidens -- well, beautiful women. And that's before he enters a royal world that is truly fantastical.