A secret organization led by an ancient royal family is hidden behind the walls of a centuries-old castle, away from the gaze of the world. The kings have reached elderly age and are looking for heirs. They understand that they can dominate countries, but not their children or time. Their daughter Nesia, whom they know nothing about, has been wandering the world for almost 20 years. Their son Henry is adamant about not returning to the castle and continuing the family duties; instead, he has dedicated himself to his medical career and lives in America. Their grandchildren lived regular lives, oblivious to their royal heritage. The castle's rulers feel it's time to look for someone to take over their responsibilities. Henry's son is a student and is unaware of his grandparents' past. Nesia's daughter knows nothing about her family background because she was raised by Nannies. Grandchildren Max and Mary, ignorant of their grandparents' true objectives, are subjected to a series of behind-the-scenes tests and tasks designed to test their knowledge, intelligence, and bravery.