Because of he and his friends' vital intervention in uncovering the plague conspiracy in the previous book, Christopher and company are invited to meet King Charles. It is on this special occasion that Christopher actually saves the life of the king and is sent to travel with his sister back to France to uncover the plot to murder the descendants of a previous French (can't remember which one) and keep his sister alive. While investigating he learns of a sacred mission of the Knights of the Templar and a great lost treasure.

Middle school.