When Elizabeth, a reclusive historian, is found drowned in a tributary of the River Cam, she is clutching a glass prism and has left behind her unfinished magnum opus, a book on Isaac Newtown's alchemy.

Her son, Cameron, turns to Lydia Brooke, a young writer and friend of Elizabeth's and asks her to complete the last chapter of the book.

Lydia hesitantly agrees and moves into Elizabeth's strange house, where she soon finds herself entangled, not only with Cameron, but also with a four-hundred-year-old murder mystery, a network of seventeenth-century alchemists and a ghostly figure intent on disrupting her work.