Recapping from the previous episode, the figure who Jestro gave the Book of Betrayal to is revealed to be Clay, who takes Jestro to the Fortrex. When the Book of Monsters attempts to gain the Book of Betrayal and Jestro, the Nexo Knights split up as a diversion until Clay is cornered. Now fully reformed, Jestro sacrifices himself so Clay can escape with the Book of Betrayal. The Nexo Knights then stage a rescue mission to save Jestro from the volcano lair where the Book of Monsters reveals that he is actually the dark necromancer Monstrox, whom Merlok turned into a book and divided his power among eleven other spellbooks. Monstrox adds that he needs Jestro as a host body to regain human form through a ritual in the "Dark Arena", waiting for the Book of Betrayal to corrupt the Nexo Knights. Unfortunately, Clay appeared to have succumbed to its power and begins to bring the Book of Betrayal to Monstrux.