The plot of the book is based on ancient Celtic myths about changelings. Changelings, according to legend, are creatures that evil spirits leave to their parents in return for kidnapped human children.

The heroine of the book is a girl. Patricia (Tris). She has a mother, father, and sister Penelope. A seemingly ideal family, a seemingly ideal home... Everything seems to be fine, only one day Tris wakes up and feels that she is “not herself.” Her head feels like it’s made of cotton wool, she’s hungry all the time, her sister looks at her with hatred and calls her “fake,” dolls and mannequins talk to her... Her parents try to explain the oddities as a normal fever. But Tris understands that everything is not so simple. She went crazy? Or is she really not real? One day she overhears a conversation from which she learns that the “real” Patricia was kidnapped, and she is just a substitute doll, consisting of branches, leaves and the diaries of the kidnapped Tris. Changelings can only live 7 days, but then what? Death? Patricia needs to find out this in order to be saved.

Mysticism, fantasy, thriller, detective story - it's all in the book. But there is also an ordinary family, with problems familiar to everyone, there are sisters who fight for the attention of mom and dad, there are mom and dad who refuse to understand their children and believe that the main thing is not to let their daughters go anywhere. There are problems and sorrows that are familiar to everyone.