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.