In 1903, Louisa, an impoverished young widow, goes to Glastonbury to care for her ailing aunt. One day while sitting beside the ruined abbey church, she experiences a vision from the past of a woman who was guardian of one of the three sacred wells on the Isle of Avalon - the red and white wells situated at the foot of the Tor are known to this day, but the black well, which reveals the future, has lain unrecognized for centuries. Further visions follow revealing the lives of the women whose gift of seership marked them out as keepers of the dark well. Louisa has suffered great tragedy in her life and believes that love and happiness are no longer for her, but as she learns of her deep connection to the women of the dark well and the gift she shares with them, her life takes an unexpected direction