Achtriel is a prodigious, but solitary, foundling living near Rouen in the seventh century AD. With her adoptive grandfather and his lively circle of friends, she has grown up well-educated and independent. But changes in her environment require her to adapt to new and often difficult circumstances. One of these is the addition to her household of a mysterious and beautiful older girl, Tirzah. Achtriel's struggles with Tirzah, as well as with her own limitations, bring more contact and conflict with the wider world.