Bad Mermaids: Meet the Sushi Sisters by Sibeal Pounder

Illus. by Jason Cockcroft. Bloomsbury Children's Books, 2020. ISBN: 9781526616883.
(Age: 7-9) Recommended. The fourth book in this amusing series introduces Meri Pebble (the best spy mermaid in the Fortress Bay spy school, according to Meri anyway!). Meri pesters her supervisor into giving her a new mission and she is tasked with uncovering what is behind a crabogram that says the Famous Sushi Sisters are going to destroy all the humans. She and her friends - Beattie, Mimi and Zelda, (aka the Bad Mermaids) go undercover as a personal assistant and the GLAM squad to show that there is no truth to the idea that the Sushi sisters would even consider harming any humans. Meri is sure she can prove them to be the famous and seriously spoiled mermaids who just do pranks for their TV show and nothing more. But the mermaids soon realise the Sushi sisters are up to something and wonder how the sisters got their hands on some very strange pets like their mercats (half mermaid half cat) and hamstars (half seastars half hamsters).
Meanwhile their human friend Paris is moving from California to a castle in Scotland which boasts a loch haunted by a mermaid. Paris' mother has given up making socks and taken up selling mermaid make-up to humans under the brand name Flubiere. She has even brought a tankful of Puffer fish to promote her brand to the fish-loving people of Scotland. Paris befriends the mysterious mermaid in the loch and helps her Bad mermaid friends in the process.
The books all have delightful references to all things fishy that young readers will enjoy. The lessons about being a good friend and not getting taken in by the glamour and glitz of famous people are carefully woven into the story as Beattie learns the hard way that being the cool girl with the Sushi sisters is not all it promised. Themes: Espionage, mermaids, seahorses, magic, friendship.
Gabrielle Anderson