The year is 1557. The royal ship Tre Kronor is on a secret mission. Its destination: the legendary island of Rulantica, where the source of life is said to be found.

Like all the sailors aboard, ship’s boy Fin hopes this unique mission will bring him honor and fame. This only makes his disappointment more bitter when he has to stay on board while the captain and other sailors head to the island to find the source and to fill their water.

Fin secretly goes to the island to beat the captain in his quest and prove to everyone that he is more than a simple ship's boy.

As he travels on his journey he falls in love with the mermaid Kailani, which eventually leads him to the source of life. Almost at the end of his quest he learns that the plundering of spring water would mean the end of the island.

Will he abandon his grand goal in order to protect Rulantica and its mysterious inhabitants from the captain's unbridled greed? Torn between the prospect of fame and his growing affection for Rulantica, Fin sparks a battle for love and justice.