A smart first-year med student takes nothing seriously, except the pursuit of his Gross Anatomy (human dissection) lab partner. It's up to her and their teacher to find a way to convince him to take his studies and life seriously.

In Boston of 1691, a warlock is sentenced to death, but escapes magically into the future (our present), followed doggedly by the witch hunter. There he is searching for the three parts of the Devil's Bible, trailed by the witch hunter and the woman whose house he landed in. They must stop him, as the book contains the true name of God, which he can use to un-create the world.

Morgana, sister of Ursula, almost steals the baby Melody from her parents, Ariel and Eric. To protect Melody, she's told never to enter the ocean, but by her 12th birthday, she's been swimming there for years. She discovers the magic locket that was to be her christening gift, which makes her visible to Morgana. Morgana tempts her by offering her fondest wish, to turn her into a mermaid; however, to remain a mermaid, she'll have to steal the magic trident from King Triton (who, unknown to her, is her grandfather). Meanwhile, all the sea creatures are searching for her. Along the way, she joins up with comic relief sidekicks Tip (a penguin) and Dash (a walrus). When she returns with the trident, Morgana's evil nature is revealed, and there is a massive battle of good and evil.