When she incurs Neptune's wrath by finding a diamond ring buried under rocks in the ocean, Emily is put under a curse that will force her to choose to be either a mermaid or a human and split up her parents forever.

A class trip to a beautiful island is overshadowed by a local myth about a mysterious ship that may have ties to the lost city of Atlantis.

Neptune, King of the ocean, sends half-mermaids Emily and Aaron to the land of the midnight sun to investigate the source of the dangerous storms brewing in the ocean.

On the night of the blue moon when mermaids are said to gather on a sandbar in the Gulf of Mexico, ten-year-old Keeper sets out in a small boat, with her dog BD and a seagull named Captain, determined to find her mother, a mermaid, as Keeper has always believed, who left long ago to return to the sea.

"The Princess in Black and her friends are enjoying a day of sun and sea on Princess Sneezewort's royal boat when a real, live mermaid princess emerges from the waves! Eeeeeee! Princess Posy needs their help protecting her very cute sea goats from being eaten by a very greedy kraken. But the princesses and the Goat Avenger quickly realize that fighting underwater can be tough for land dwellers, and only the mermaid Princess Posy can save the day....

Little Scallop, a princess of the Mollusk tribe, longs to have a real adventure. So late one night, she and her mermaid friends sneak off to dive for pearls. They run into a fierce storm and a strange ship sailed by men who would love to capture a mermaid.

The desert is no place for ocean-dwelling Kampii like Aluna and Hoku, especially now that Aluna has secretly started growing her tail.