Three celestial bodies and an aliorn for each but while those of the sun and moon are known throughout Equestria, the one of the planet itself is rather mysterious. Terran is the middle brother of both Luna and Celestia and ruler of his own land and is waaaay overdue for a social call to his sister's kingdom. A visit is needed for a catchup, to ask for their help in locking away an ancient evil and to explain to his daughter why he wasn't there to give her away at her wedding........