Captain Sharky and his crew embark on an exciting adventure in the deep sea. According to a legendary tale, a valuable treasure lies in a sunken city there. With the help of a self-built diving sphere, they descend into an impressive underwater world. However, in the darkness of the ocean, not only friendly fish await them: a gigantic, wild sea serpent feels threatened by them and attacks mercilessly. Will Sharky and his crew survive the fierce battle unscathed?.