In an alternate Edinburgh of 1824, every woman lives in fear that she will be the next one hanged for witchcraft. All it takes is invoking the anger, or the desire, of the wrong person. Nellie Duncan, beautiful and unwed, keeps to herself until she encounters the Rae Women's Apothecary. There, fiery Jean Rae and the other women provide cures and teach others that they too can aid the winter deity, the Cailleach, embracing her characteristic independence, agency, and craft, in turn becoming witches themselves.

Nellie finds a place and a purpose at the shop, and a blossoming romance with Jean, as she learns about nature-based craft and a witch's ability to return to life after death. But the Cailleach has an ancient enemy intent on stripping the power of the deity and all her witches, leaving a wake of patriarchal violence and destruction. When heartbreaking disaster strikes, Nellie flees and spends the next two centuries hiding from the world—until love gives her the courage and the motivation to come back.

Nellie's past is waiting for her there, and hanging witches is no longer the only means of oppression. But this time, Nellie refuses to run—either from her foes, or from her resolve to awaken others to the unimaginable power that can come with fighting the patriarchy in its many forms—and finding one's own magical inner strength.