There are no concrete details about the plot yet, but much like how the first two seasons corresponded with the first and second books in the trilogy, the third season of A Discovery of Witches will follow the plot of The Book of Life, the final book in the All Souls series of novels by Deborah Harkness.
With Diana finding out that she was pregnant near the end of the show’s second season, the couple will be dealing with a lot when they return to the present day. In addition to having their hands full with the pregnancy and impending parenthood, they’ll also be facing off against Knox, who still wants Ashmole 782. Meanwhile, there is still a threat from the Congregation, which is made up of witches, vampires, and daemons, as it still forbids mingling between the three kinds of supernatural creatures. Something tells us they won’t be too happy to find out that Diana is carrying a child created by a witch and a vampire.
As if that isn’t enough drama already, new enemies will also make themselves known, and the subject of Matthew’s vampire blood rage, a major plot point in the third novel, should receive significant attention in the final season, especially after Domenico survived an attack from a blood-rage vampire at the end of season 2.
It’s a lot to fit into a single season, but after the success of the first two, there’s no reason to believe the writers won’t be able to make it all work.