Corin, Soren and the other owls of the World's Finest Beak set out on a journey along the River of Wind in search of a legendary kingdom inhabited by the mysterious blue owls. Meanwhile, Eglantina and Primrose, flying around familiar territories, learn terrible news. It turns out that Nira, at the head of a detachment of Pure Ones, also found out about distant lands and decided to go in pursuit of the Night Guardians in order to take them by surprise on foreign territory. But no one even suspects what surprises an acquaintance with blue owls will bring and what dangers await the Great Tree after the arrival of Striga, one of the blue owls of the Middle Kingdom.