Sirenetta, the little mermaid, has been living on land for a year now. When four lost mermaids come to her for help, Nettie must dive back into the sea she left behind. Nettie and her four finned friends will have to be careful; there's a wicked Pirate Queen hot on their tails.

Nettie, a modern Little Mermaid, is living humanly-ever-after in Provincetown with her fiancé, Freckles. When an anxious young merperson named Archie and Calypso the Sea Nymph come looking for help though, the part-time mermaid dives back into action. Together, Nettie and her three friends travel the world in search of the Terzetto Treasure; a magical artifact that will stop an evil sea witch and her coven from draining the ocean of life.

Sirenetta's boyfriend is finally meeting her family, but there's just one little problem; he's a human and they're all mermaids.