When Molly Holmes moves with her family to Horseshoe Bay, her grandmother gives her an enchanted shell necklace that magically transforms her life. The power of the necklace transports Molly to the Undersea Kingdom, where she discovers that she is a Secret Mermaid and meets lots of new mermaid friends. But the evil Dark Queen Carlotta seeks to steal control from the good Merqueen Luna, by seizing the magic pieces of conch shell that help protect the...

Casper, the cocky new boy at magic school, challenges Oliver Moon to a scary spell-off, and Oliver is worried even his trusty magic wand will not help him get out of trouble.

In the climax to the mermaids' search for their pieces of the magical conch shell, Molly finds herself in the frozen seas of the Arctic. There she discovers that the Dark Queen has stolen the last conch piece and imprisoned ice mermaid Shivana. With the help of a friendly walrus, Molly rescues Shivana, and, dodging an attack by an enchanted polar bear, they set off to confront the Dark Queen in her distant lair.

Oliver's class is going on a school trip to a haunted house museum and Oliver is really excited about the ghosts he might see. But he didn't plan on the swarm of vampires that arrive in the middle of the night. Can he and his friend Jake work out a way to save his classmates from the bloodthirsty bats?

As Molly's underwater quests begin, she must help fellow mermaid Ella recover her piece of the magical conch shell in order to protect the coastline and prevent floods. But the Dark Queen's army of menacing sea creatures is hot on the mermaids' tails.

"Swimming with the turtles and tropical fish in the ocean reefs has always been such fun for the mermaids, until the reefs begin to die. Molly must help her friend Coral find her magic shell so she can rescue the reef -- but the wicked Dark Queen and her army have other plans..." -- Back cover.

Molly is called back by the Mermaid Queen because the mermaids desperately need her help. All the whales, turtles, seahorses, octopuses and dolphins have vanished from the seas and the mermaids expect dark magic is at work. Molly believes the answer to their whereabouts might lie in a strange sparkly ball she spotted in a rock pool.

Secret mermaid Molly must help her mermaid friend Delphi to find the second piece of the enchanted conch shell in time to prevent a terrible oil spill.