All Ava Adair wants for Christmas is an uneventful holiday season with her merman mate, Carter Stevens. But when her family plans a tropical Christmas vacation to the Whitsunday Islands in Australia, Ava must break mermaid tradition and relocate all the merpeople in the sea down under to celebrate Summer Solstice instead of the much anticipated Winter Solstice. Luckily for the new mermaid queen, merpeople can adapt. Instead of snow angels and hot chocolate by the fire, Ava gets a deserted island full of brazenly transformed merpeople who refuse to stay submerged in the ocean, forcing her to call upon the sea for protection. After Ava's ocean magic causes a boat to sink offshore, she must figure out how to save an unsuspecting human family from a fatal fate while hosting the best solstice she can. It doesn't help that her human family wants her to remain on land. Uniting the traditions of land and sea proves harder than Ava anticipates, and she must step up as the mermaid the ocean chose her to be-or be deemed the destroyer of all holiday cheer.