The third instalment in The 39 Clues series, The 39 Clues #03: The Sword Thief continues the story of the quest for the fortune of the deceased Grace Cahill. When Grace passed away, her relatives did not easily inherit her wealth. Instead, they had to form teams to win a hunt involving clues and sans rules.
One of the teams comprises of a pair of orphaned siblings, fourteen year old Amy and eleven year old Dan. While rest of the teams are rich and have different means to unravel the clues, the siblings have nothing going for them. They are, however, determined, smart, and united.