As events culminate in Forbidden Treasure with Ethan Jameson's escape from the jungle, Fionn and his fellow spider monkey Shifters embark on a journey to Terra do Diabo, a Milesian stronghold, where they believe the reincarnation of Mil has landed.
Born and raised in poverty and criminal activity, Fionn has always been a violent man, even worse after being converted into a Shape Shifter—he is one of the Matadores, the only ones standing between the infectious Village Eaters and the survival of this world.
Though determined to sabotage the prophesized Sons of Mil battle, Fionn soon finds himself battling monsters, protecting Xoana and her little sister after they shipwreck, and battling his own conflicting emotions as his path now leads him towards the portside town of Pássaro Azul. Despite pressure from his comrades to focus on the mission at hand, and the Ancient who wants the Shifters back, Fionn can't help but fall for Xoana as the young woman overcomes obstacles, sacrificing herself to save her sister.
Realizing everything he has been told about being a Shifter may be false, and that his ardent wish to be human again will never come true, Fionn has no other choice than to become the hero he never believed he could be.
Invincible is the first step on a whirlwind adventure that will encourage non-humans to finally fight for the rights to this world…