When three teenagers discover a set of dinner plates with a mysterious floral pattern, they inadvertently trigger a cycle of ancient, tragic Welsh mythology that threatens to consume them. Alison, her stepbrother Roger, and the local boy Gwyn find themselves trapped in a reenactment of the legend of Lleu Llaw Gyffes, Blodeuwedd, and Gronw Pebr. As the supernatural forces of the valley exert control over their actions, the trio must navigate the volatile tensions of their own burgeoning identities and social class differences. The narrative unfolds through a tense, atmospheric lens that blurs the line between the mundane present and the inescapable weight of the past.

This work is widely regarded as a seminal piece of twentieth-century fantasy that challenges the boundaries of the genre. Critics frequently highlight the narrative's ability to weave ancient Welsh myth into a modern domestic setting without losing its unsettling, psychological edge. The book is often praised for its complex character dynamics and the way it treats its young audience with intellectual maturity. It remains a fixture in discussions regarding the evolution of young adult literature and the power of folklore in contemporary storytelling.