A deadly disease has wiped out millions of Ulums, the winged inhabitants of the planet Demoth. Fay Smallwood, the daughter of a world-famous doctor, comes to the conclusion that the epidemic was deliberately provoked. She joins the “Vigilant Eye,” a group of independent experts investigating a terrible crime, and during the investigation it turns out that the Ulums are by no means the first settlers on the planet and somewhere in the north, in long-abandoned mines, samples of technologies are stored, the owner of which reaches peaks of power.