It's the day of graduation for the latest class of Nexo Knights, but all does not go as planned as the court jester Jestro decides to use the Book of Monsters to get the respect he deserves.

Power is restored to the kingdom, and Jestro is on the loose. He gains the Book of Evil, transforming into a true villain. Meanwhile, the new knights are having trouble working together to protect the kingdom amidst the chaos from Merlin's demise.

The knights work on their teamwork while the royal RV is converted into the Fortrex, the new headquarters for the knights and a home for Merlok 2.0 and the Nexo power.

Jestro finds the Book of Chaos, and gains chaos monsters to summon, but they won't listen to him. The knights have to stop those monsters while protecting the king and queen, who are giving a tour of the kingdom to business leaders.

In the town of Spittoon, everyone is afraid of everything thanks to the Book of Fear. The Book of Monsters eats the book, releasing Whiperella, whose whips spread a person's worst fear with a single strike.

Lance earns a leading role in 'The Golden Castle' and his friends play in the background. Macy declines but then eventually agrees to do so. When they're filming, Jestro summons a monster called Lavaria, a very sneaky monster; Jestro then takes a liking to her and orders her to find and give the Book of Monsters to eat the script of 'The Golden Castle' and hold its power, which they successfully do. But soon the knights find out, and they get the new Ultra Armour, giving them more powerful weapons, whilst the director is directing all the action.

The knights' go to Axl's home town, Digginton, where they meet his mother, father and little sister, Axlina, who instantly takes a liking to Robin. Soon, they leave to find a new book called The Book of Deception in a massive maze, which doesn't look like what it seems. They eventually find out that Jestro and the Book of Monsters are searching for it too, and it turns into a race to get the book first.

Leaving the maze with the real Book of Deception, Jestro feeds several books of the same kind to the Book of Monsters to create the fake NEXO Knights. They raided and destroyed the city of Bork. The real knights come and all the citizens shooed them off for something they didn't do. Ava and Robin hear the news and are shocked by what they did. The monsters trick the citizens again by turning the Evil Mobile into the knights' Rolling Fortrex. When they tried to raid again, a Black Knight blocked their way and defeated them with ease. King Halbert then contacts the knights and said that if they don't come up with any evidence that they didn't destroy the cities, he'll be shutting them down. Several times the fake knights tried to attack a city, the Black Knight is there and defeats them in less than a few blows. The real knights came in afterwards in the real Fortrex and conquered over their fake selves. Soon, they come to the fact that Robin was in fact the Black Knight in disguise!

Jestro and the Book of Monsters travel to the place where the evil wizard Morstrux did his evil deeds (?) and find the Book of Destruction. Soon, Jestro brings out a whole lot of destructive monsters and split up in different directions. Macy scolded to her dad that she quits being a princess, but he disagrees and that she was born to be a princess (?). When the knights find out that monsters are attacking, Merlok 2.0 told them that they should go together, but they decided to split up; King Halbert hopes her daughter will come back. However, the knights get captured one by one, with no way to escape. When all the monsters were asleep, Aaron quietly escapes, being the only knight to save all his friends before Jestro attacks the castle of Knightonia.

Aaron must figure out a plan to save all his friends. Meanwhile, Macy has a flashback, saying that she wanted to become a knight, not being a princess all the time. Soon, she admitted to herself that she was not ready to be a knight, but was cut off by Aaron, who used his energy bow to cut the chain off of her, and retained her shield and mace back. The two then rescued Clay, who was chained on a target, getting spun around all the time. After him, they saved Axl by giving him a chain of sausages to climb up, but was unsuccessful the first time, and the second time, they succeeded. Finally, they rescue Lance, who was stuck in an animal farm, making a new friend, called Hamletta, a pig. Jestro, who was so close to victory, were stopped by the knights, and the rest sans Clay, got their NEXO Power, and the blue knight got one that was last done ages ago. When Clay got the new NEXO Power, one smash of his sword and all the monsters turned to purple dust, and he slammed his sword down again, and sent Jestro all the way out of the kingdom of Knightonia. Near the end, King Halbert apologizes to Macy, and he claims her an official NEXO Knight. Lance then gets Dennis back on one condition: Lance has to be the servant of Dennis for a week.