Two girls, two worlds - a story with one foot in the modern world and the other in myth, legend and poetry. Seren is 14 years old and lives with her nain, having lost her single-parent mother to cancer. An only child, scarred by this early bereavement, she struggles at school. Heledd, a girl who exists in the 7th century AD and whom Seren meets in her dreams, has her own struggles in the aftermath of the Mercian war, which left almost everyone dead. Together, they help one another survive.