Kellian is a boy who is kidnapped from his family when he is about five years old. He's brought to the castle in his city, where the king and queen of his country live; their son, the prince, looks a lot like Kel. They make Kel the "Sword Catcher" for the prince, a traditional stand-in for the prince at public events, to become the target in case anyone attempts to kill the crown prince.
Kellian grows up with the crown prince, whom he discovers is a terrible person.
The series will cover Kellian's life up until he is twenty-three, twenty-four, which is when the story really starts.