For where your treasure is, there will your heart be also, even at the bottom of the sea.
Frederick the Seahorse loves to scour the ocean floor, looking for the Titanic’s lost sea chest. Although Frederick’s father King Maris, and his father before him have ruled the Kingdom of Kaimana they have not been able to find the lost treasure. Afraid of running out of treasure and losing his kingdom like Uncle Makai, Frederick, an only child and next in line for the throne, insists he must find the treasure so as not to be overshadowed by their rich neighbor King Saewine and his sons. King Maris tells Frederick to make sure he doesn’t squander the wealth he already has and that it would be better for Frederick to find a bride and start a family. But Frederick longs to have as much treasure as possible, so that statues are made of him, similar to those of his father and Poseidon, God of the Sea.
Later that night, when the ocean grows dark, Frederick sets out on an expedition without his father’s consent. He writes a note on a seashell, and when his father finds it, the King weeps in remorse, fearing that Frederick will die in search of a vain treasure chest. After weeks of swimming past sharks in the fierce ocean waves, Frederick washes ashore on an unknown island. When he opens his eyes, he finds himself lying next to a sea chest of treasure, guarded by pirates with sharp swords. Frederick begs to go back to his father. But the band of pirates wraps Frederick up in ropes and weights, takes him out on their ship, and bounces him off the plank. Frederick sinks to the bottom of the ocean. In order to taunt him, the pirates drop a shiny diamond with Frederick, which lands at his nose on the ocean floor. Just as he is about to give up hope, he thinks he is having a vision: A gorgeous red-orange seahorse named Naia saves Frederick’s life by unraveling the ropes secured by the pirates.
Frederick explains to Naia that he has been searching for the sea chest from the Titanic. Stunned, she says she enjoys the ocean’s beauty more than an old chest from that sunken ship. Frederick notices how beautiful Naia’s blue eyes are in the sunlight. Leaving the pirates’ diamond behind, he asks her to come with him to meet his parents. Naia asks her friend Guppy to send word to her father that she will be gone for a few days. She tells Guppy that it’s finally true love. After days of swimming in the ocean, Frederick and Naia dance in the waves to more than one melody. Trying to nudge Frederick into admitting that he admires her, Naia asks him if he has a seahorse in mind to be his wife. When he says “no” and that he’s trying to acquire wealth first, Naia swims back to her father, despite Frederick’s protest. Days later when Frederick finds her in an ocean cavern with her friend Guppy, he’s afraid she won’t even speak to him. After desperately apologizing, Naia forgives Frederick. When the two seahorses swim to King Maris’ throne, the King and Queen are speechless at their arrival. Frederick asks Naia to marry him and a tear fills Naia’s eye as she kisses him, knowing she loves him more than anyone—even her father, King Saewine, the richest king in the ocean.