The Serpent's Mirror Wikia

Viking Penguin's announcement of the series on October 9, 2015 said:

"Deborah Harkness has placed World rights to her fourth novel, THE SERPENT'S MIRROR, with Viking Penguin and editor Carole DeSanti. Set in the All Souls’ world and centered on Matthew Clairmont’s career as a vampiric double agent in the Tudor era, the novel explores historical riddles surrounding the ascent of Elizabeth I to the throne. A contemporary narrative involves the witch-historian Diana Bishop and the cast of the Harkness’s bestselling All Souls’ Trilogy (A Discovery of Witches, Shadow of Night, and The Book of Life). THE SERPENT'S MIRROR is projected as the opening volume of a series of novels drawing from material in the centuries-old de Clermont archives, and a 2017 publication is planned."

From Deborah Harkness:

"I'm sure you will have *many* questions and in the upcoming months I'll probably have the answers, but for the moment this is as much as I can share. You will, as ever, get all the news here, on twitter (@DebHarkness) and on my website so stay tuned for further updates with foreign editions, publication dates, covers, tours, and more. Until then, I hope you will join me in celebrating the return of our favorite characters--and the introduction of a few new ones, too."