Phineas and Ferb visit the Greek Museum, While Phineas is admiring a statue of Perseus, Medusa's head brakes off and hits him in the head. Phineas dreams he is Perseus, a simple peasent in the city of Joppa. Perseus has a crush on Princess Andromeda (Isabella), and while trying to sneak in the palace to see her, he discovers the banished prince, Calibos (Buford) plots to release the sea monster known as the Kraken and use it to destroy the city. He teams up with Andromeda, the winged platypus Perrisus (Perry), and the poet Ammon (Ferb). Together they must capture the gorgon Medusa (Candace), and use her powers to destroy the Kraken.
Perseus (Phineas)- A brave and kind fisherman, trys to thwart Calibos' plot against Joppa, to win the heart of Princess Andromeda.
Andromeda (Isabella)- A spunky princess who attracts Perseus.
Ammon (Ferb)- A wise yet silent poet.
Perrisus (Perry)- A winged platypus who was Calibos' prisoner, until rescued by Perseus and his friends.
Calibos (Buford)- An arrogant prince who was exiled for killing an entire herd of winged platypuses (except Perrisus), as revenge he plots to release the Kraken and use it to destroy Joppa, and make a new kingdom for himself, when Perseus trys to stop him he trys to plague his quest with monsters. He has a crush on Andromeda, but she has no interest in him.
Medusa (Candace)- A cranky gorgon who has the power to turn people to stone with one look, Perseus and his friends need her powers to defeat Calibos' Kraken. Perseus promises her fame for saving the city, so she offers her services.