No need to get up early and do homework every day! Amy, Flora, Fau and Franek go to the village of Frog Horn to see Amy's grandmother. Summer in a house by the river is wonderful: you can have fun in the garden, walk among blueberries, build a smokehouse and go horseback riding. But there are no holidays in the Secret Club of Supergirls! After all, books are disappearing somewhere from the library of Zabyachy Rog. I wonder if it was the bookworms who tried, or if someone deliberately decided to harm the book collection? Our friends are getting down to business! Will they be able to unravel this mystery as well? Read already in the fourth part!