On her 13th birthday, Molly learns the truth about her mermaid heritage in this series opener.Molly Seabrook and her four sisters live in a lighthouse and work in their mother's fish-and-chip shop. Molly's job is to dress up as a giant haddock and pass out flyers advertising the shop to people on the pier. It's not a job that guarantees her any popularity, and Molly's a frequent target of the pretty, blonde class bully. On the night of Molly's birthday, her mother and older sisters drag her down to the water's edge and let her in on the family secret. Now that she's come of age, Molly will sprout a tale and gills whenever she gets too close to large bodies of water. But unlike her sisters, who adore being half-mermaid (their long-absent father is human), for Molly it's just more fuel to the fire of her self-loathing. How can she ever be popular, or even just ordinary, if she becomes a big, helpless, floppy fishgirl every time she gets too near unexpected water? Molly's adolescent miseries provide a believable note of heft in an otherwise-lighthearted tale full of fart and puke jokes. Clunky Americanization of this book first published in the U.K. in 2019 adds confusion but does not materially detract from the humorous charm. Most characters are white, and Molly's best friend is of Chinese descent.Delightful froth with just a touch of early-adolescent angst. (Fantasy. 9-11)