The Convert (1987)

From the back cover: "What turned the prince into... THE CONVERT? Capital city is happy, prosperous, and secure - until the king's son returns home after a long adventure. his new beliefs become new laws, and the trouble that results might destroy the kingdom. The characters, fleeing for their lives, must find out what really caused the Prince's conversion, and restore his sanity before the kingdom falls. The Convert features both wilderness and dungeon adventuring, with details on two non-human societies. It was originally used in 1985 as a major tournament at the world's largest gaming convention. And now this fully revised and updated edition is available for you to use at home."