He next travels to Caladan to meet his descendants ; soon tragedy begins to befall the Atreides .
Vorian realizes too late that Griffin and Valya 's younger sister Tula has visited Harkonnen vengeance on descendants .
He next travels to Caladan to meet his descendants ; soon tragedy begins to befall the Atreides , and Vorian realizes too late that Griffin and Valya 's younger sister Tula has visited Harkonnen vengeance on them .