Aspiring costume designer Katie gave up everything in her divorce to gain custody of her fearful, faithful rescue dog, Barkimedes. While figuring out what to do next, she heads to Florida to live with her grandmother. Katie quickly learns there's a lot she doesn't know about Nan - like that she was a mermaid performer in a roadside attraction show, swimming and dancing underwater with a close-knit cast of talented women. Although most of the mermaids have lost touch, Katie helps Nan search for them on Facebook, sparking hopes for a reunion show. As her college love Luca, a documentary filmmaker, joins them, Katie struggles to balance her anxiety with her hopes.