Season of the Witch tells the story of Gabriel Blackstone: hacker, information thief, and skilled "remote viewer." Asked by a former lover to investigate the disappearance of her stepson, Gabriel’s suspicions fall on Minnaloushe and Morrighan Monk, two beautiful sisters who live in a rambling Victorian house in London. Independently wealthy, the sisters spend their time dabbling in alchemy and the ancient Art of Memory—invented by the Greeks and used by alchemists and magi such as Giordano Bruno and Leonardo Da Vinci. The sisters are white, or "solar," witches, who aim to use alchemy not to turn lead into gold but to attain ultimate knowledge and therefore ultimate power. Gabriel soon becomes convinced that his client’s son had been murdered and that one of the women is the killer. But which one?

As Gabriel infiltrates the world of the sisters, he finds himself drawn inexorably deeper— becoming entranced even as he realizes that he is in mortal danger. When he is caught snooping, Gabriel must race to unlock their secrets before they can retaliate. To save himself— and the one he loves, presuming she is not guilty—Gabriel will have to fight one of the sisters within the landscape of her own mind.