Nimona, a young shapeshifter with a knack for villainy and Lord Ballister Blackheart, a villain with a vendetta, set out to prove that Sir Ambrosius Goldenloin and his friends are not the heroes everyone thinks they are. But Lord Blackheart soon realizes that Nimona's powers are as murky and mysterious as her past and her unpredictable wild side might be more dangerous than he is willing to admit.