When the Longs attend a Florida family reunion, Jake must deal with both his annoying cousin Greggy and a crime syndicate of shark terrorists plotting on flooding half of the continent.
The Longs are preparing to attend a family reunion, and Jonathan is enthusiastic about the occasion, except for Jake, who begs his father to not let him come to his Aunt Cathy's reunion this year after a couple of years being with the table of all the younger kids of the family, whom Jake is annoyed, especially his Cousin Greggy who is a snot-wiper. And so Jake wants to be part of the adults' table since he is the oldest at the kids' table, but Jonathan tells him that unless one of the adults cannot attend he cannot join them. Suddenly, Haley arrives with bad news, that Uncle Lee had suffered from Appendecitis but is in good condition but not be able to make it to the reunion. Jake is glad to hear that, now he has the chance to seize a spot from the adults' table.
Meanwhile, Susan asks Lao Shi a big favor to take care of Jonathan away from the reunion this year, as she is still not confident that her husband can handle the truth of her family's side. She has missed many of her family's reunions as a result, she didn't even enjoy her wedding reception as she still has to keep him away from her family's magic dragon powers. Jonathan are excited to go to the reunion, so is Jake whom has never been happy to go to the reunions before. The family reunion is located at their Aunt Cathy's owned island at Florida Keys, from there, a group of crime syndicate of sharks are planning to find something special in the island.
Hours later, the Longs arrive at Aunt Cathy's home except for Lao Shi, who is stuck with Jonathan for a few days, where Lao Shi and Jonathan are navigating their way to Florida by car, while Lao Shi also orders him to drive in wrong directions, causing Jonathan to scatter around the country. When Aunt Cathy complements Jake that he's a 'big handsome man' and tells him that he has a special seat for him, Jake thinks his about to be put into the spot of the adults' table. To his surprise, he is still stuck with the kids' table, Haley tries her best to respect the kids' nasty behavior, even after she got hit by butter in the head by one of the kids. Jake is surprise to discover that his Cousin Greggy (now called Gregory) is now at the adults' table, despite being a year younger than Jake, he learns that he is now able to use his dragon powers, so being a mature 'adult' to the family's perspective. Despite this, Jake rushes towards Gregory and loudly complains about being stuck in the kiddie table. But the family still mocks him of being a kid, and is force to go back to the kids' table.
Meanwhile, Lao Shi and Jonathan have ended up in Western Kentucky, and Jonathan has doubts about Lao Shi's navigation. Lao Shi tells him that he thought Jonathan would want to see the world's largest turkeys. Jonathan is then attacked by a group of turkeys and retreats to the car.
At Aunt Cathy's, after Jake does the dishes, his cousin Gregory tells him the only way to get the spot at the adults' table is to prove that his the only young dragon who counts and overpower Gregory. Jake confidentially challenge Gregory's powers and prove he mastered his dragon form, if he loses he'll be stuck at the kids' table and Jake gets the spot at the adults'.
The next day, they face-off in the beach where Fu is the referee, Gregory is first to come up with a challenge and he chooses to test his fire breathing skills. In basic training, Gregory fires a small fireball while Jake's burst a huge one and devours Gregory's, earning Jake the first point. From afar, Susan and Cathy watches by, and Cathy soon has a competitive feeling cheering his son to overpower Jake. It's Jake's turn to decide the next challenge, and he chooses their ability in speed flying, a one lap around the island in the count of three. But Gregory goes for a head start, but despite that, Gregory is still having trouble with flying. Jake flies around the island at blazing speed, spinning around the island already a few times while Gregory is still making progress to his first lap. When Gregory finishes his lap, he claims that he won as he recall that Jake said only one lap around the island, and Jake did it many times resulting him to be disqualified. Jake accepts and gives him the point.
When Gregory is about to give his challenge, a female magical shark arrives and seeks help from the dragons she saw on the island, but Gregory sees her as hostile and scares her off, much to Jake and Susan's dismay. The family thinks she fought off an enemy threat that save their lives, making Gregory claim he earned another point and wins their face-off, resulting Jake again to be stuck in the kiddie table.
Later, Jake and Fu Dog are traveling underwater in search for the shark lady prior who seek their help, also for Jake to take a break away from the family. They are bothered by Gregory jet skiing near them, and Jake lashes out on Gregory to the surface, causing his magical air caps to dissapear. Jake is then pulled down from the water, but Gregory sees it as a joke and leaves the scene. He is being pulled by the lead shark syndicate named Tiburon, Jake is suffering from suffocation as he is unable to breath underwater, Tiburon demands Jake to tell him what he knows for information of what they are looking for. Jake breaks free from Tiburon, but is now pursued by the sharks. Fu Dog passes him a magical air cap, allowing him to breath again. They barely manage to escape, and is meeted by the shark lady again.
They return to the island and talk near the dock, the Shark Lady tells Jake and Fu Dog, that despite the fact they are known to have jagged teeth and bloodthirsty, they are actually are a peaceful race. Until, the shark lady shows her shark instinct by eating anything, as she cannot fully resist it. The shark lady tells them the reason why'd she needs help, is that Tiburon's shark armada are planning to seek Neptune's Trident in order to control the seas, by creating a massive tsunami that will put half of the land of North America underwater for Tiburon and all the other sharks to rule, as though they can walk through land, they have to come back to the ocean eventually to live. The shark lady tells them also, that they'll never find the Trident without her, she keeps the location of the Trident a secret, as for now, they have to find a safe place for her to hide away from Tiburon. Jake and Fu Dog agrees to help her.
Meanwhile, Lao Shi and Jonathan have traveled so far from the country that they're ending up in Alabama, that Jonathan has become irritated by Lao Shi's navigating. The two have a serious dispute by taunting each other with foreign language, after Jonathan mocks Lao Shi's mother in Norwegian, claiming Lao Shi has never learned the Norwegian language, Lao Shi's temper burst as Jonathan shockingly learns that he studied Norwegian too, and the two fight each other while driving.
Jake asks permission to his mom for a mission to help the Shark Lady, suddenly the Shark Lady's instincts kick in and could not resist the feeling and jumps in the adults' table and eats everything in sight. Gregory cowers under the table, despite her mom calling him to take action. Jake desperately pulls the shark lady away. Outside, the shark lady apologizes her inappropriate action she did, but Jake is glad she did that seeing it as a chance to finally get the spot on the adults' table, but Fu Dog tells him to stay focus. Suddenly, Tiburon's shark army arrives...
To be continued