Leonie Hastur, headstrong and lovely daughter of the Hastur Clan, most powerful of all the telepathic families who rule Darkover, is being escorted by her twin brother Lorill to Dalreuth Tower for training in the use of her psychic powers. Although this is the even she has long dreamed of - for her laran is so strong that she has been able to use it without benefit of training or the need of a matrix crystal - and she yearns for the power which will come to her if she succeeds in becoming a keeper, she is deeply disturbed. For she is plagued by a terrifying premonition that haunts her days and disrupts her nights, the inescapable feeling that something is about to happen - something monumental and dangerous which will descend upon her world and change it utterly. And all she knows for certain is that this something will be coming from one of Darkover's four moons...