A prince boards a ship, and suddenly accidently crashes and suprised to see a mermaid in the arctic. Together they board a journey together into the ocean to see waterless things, only to be pursued by the owner of the ship.
- Prince Vincent of Rome (Robert Pattinson) - a prince aboard the ship, in the end, returns home with his bride!
- Shelly (Amanda Bynes) - a mermaid and Vincent's love interest, in the end, marries Vincent, and lives life on the land!
- Ferris Von Lucas (Oscar Isaac) - the main antagonist, and pursuer of Vincent and Shelly, his goal is to steal the crown and all of Rome, and the sea , in the end, was eaten by the Sea Monster "Mungundah"!
- Gina Blessed (Helena Bonham Carter) - a ship member on the ship, in the end, was promoted, and won a trip to Panama!
- Ian Bruce (Ben Mendelsohn) - a ship member of the ship as well, in the end, gets to be with his family!
- Timothy Harris (Guy Pearce) - another ship member of the ship as well, in the end, gets a time in the Ball room!
- Captain George Vance (Ioan Gruffod) - the captain of the ship, was killed when they accidently crashed
- Marideth (Charlize Theron) - Shelly's mother, who is standing against surface dwellers, in the end, was arrested and revealed to be a traitor.
- King Socretes of Rome (Anthony Hopkins) - Vincent's father, who is hoping he might find someone in his life, in the end, Meets Shelly and honors Vincent's choice.
- Queen Amelia of Rome (Sally Field) - Vincent's mother, who is hoping for a daughter-in-law to love, in the end, congradulates Shelly.