The two kings are told that they have to try to win a competition when they attempt to arrange a treaty with an adversary island. The winner receives the reward of a princess, but Brady and Boomer discover she is not a typical princess.
After learning their father was the best warrior in island history, Boomer and Brady enroll in Kinkow Fight School. When Mason gives the kings special treatment, jealousy overcomes Mikayla. Taking Lanny's advice, she decides to test the kings' newfound confidence and skills by pitting them against Atog the Giant. But when Mason finds out, Mikayla tries to get the kings to back down, but it's too late, the kings are eager to prove their inner warrior
Boomer and Brady discover Vault 14, a secret vault which protects Kinkow's most mysterious and powerful artifacts including Duplicatus Plantus, a plant that copies anything it touches. The kings make clones of themselves and while they go surfing, they send their doubles to the Kalooki Island Peace Summit. Filling in for the brothers, the clones impress Mikayla, the island dignitaries and the other Kinkowians with their intelligence, hygiene, and professionalism. However, when Brady and Boomer overhear the clones' ultimate plan to takeover, the kings must figure out ...
It's Mikayla's birthday and Mason's brother Jason visits, but Mason isn't so welcoming due to an incident when they were kids. When the kings make Jason head guard, Mason quits and drowns his sorrows in eating. But when the Tarantula people try to roast Boomer alive, Jason cowardly runs off and it's up to Brady to convince Mason and his bloated self to come back and save Boomer. When Mason arrives, he and King Brady are captured by tarantula people. The Jason's water scooter falls on two tarantula persons, and Jason falls on other two.
In an effort to bring their holiday traditions to Kinkow, the kings promise the islanders a Super Christmas and enlist the island elves to make the toys. When the elves revolt, Boomer and Brady must figure out how to save Christmas.