It's the kings' birthday and for their royal present, they each get one wish that will come true. Right before blowing out the candles, Boomer learns that Brady has been bragging to the entire island that he is the older twin. Boomer uses his wish to find out the truth about who was born first, while Brady's wish is that Mikayla compliments him all day. Boomer travels to the center of Mt. Spew to meet with the volcano's Oracle and learn who is the older king, but the younger brother will no longer be co-king if it is known who the older brother is. So Brady, Mikayla, and Mason chase after Boomer.
Boomer and Brady discover Vault 14, a secret vault which protects Kinkow's most mysterious and powerful artifacts. They find the Duplicatus Plantus, a plant that copies anything it touches and make clone of themselves. The clones fill in for Brady and Boomer so that they can go surfing, However, clones want to replace Brady and Boomer forever.
Feeling homesick, Boomer and Brady call Aunt Nancy and Uncle Bill to check in, but accidentally end up scaring them with their tales of Tarantula people, quick sand and giant bugs. While Aunt Nancy and Uncle Bill rush to the island to bring the twins back to Chicago, Brady is accidently stung by a dangerous Waka Waka bug. With the help of Mason and Mikayla, the kings must hide Brady's strange side effects including pumpkin head and amnesia in order to prove that the island is safe enough for the kings to stay and rule. Meanwhile, Mason has a date with a girl named Stewy.
The kings must perform for the islanders at the Annual Harvest Festival, and Boomer can't wait to show off his singing skills. Brady knows Boomer has a horrible voice, but doesn't have the heart to tell him. When Brady's plan to protect his brother from humiliation backfires, Boomer discovers Brady is a terrific singer and arranges for Brady to sing to the kingdom.
Boomer and Brady meet an odd creature in the woods named Ogie (Doug Brochu). But Brady is jelous of the Ogie and is mean to him. Brady fills a void by being Lanny's friend, but Lanny's plot is to kill him. But when Boomer is invited to a feast, he isn't going to a dinner; he is dinner—or so it seems.