Nim, Jack and Alex, as well as the calm iguana Fred and the sea lion Silkie returned to their favorite island, having made new friends and many unforgettable impressions on their journey. And now the island has stopped hiding from the whole world - scientific conferences are even held here! Together with the scientists, their children come here, and one day the curiosity of the young adventurers is rewarded with an amazing discovery. But this discovery puts Nimes Island in terrible danger! Because some of the island's guests did not come here for the sake of science... And when Nim finds out what their true plans are, she will have to make difficult choices. Meet the third book about the adventures of a girl from a fairy-tale island - for the first time in Russian!