The Monster in the Lake - Louie Stowell - Bog

Kit Spencer may be the youngest wizard ever, but she sure doesn't feel like the best wizard. Her magic keeps going wrong, and other weird stuff is happening: talking animals, exploding fireballs, and a very strange new arrival in the local park. Kit and her two best friends, Alita and Josh, set off with Faith the librarian to investigate the wild magic that's causing so much commotion. Their journey takes them to Scotland, where they meet a loch-full of cranky mermaids, but the danger is greater than they imagined. Will they be able to set things right before the wild magic spreads further?