The Night Eternal by Guillermo Del Toro and Chuck Hogan

As this book opens, things look bleak for humankind: the Master has leashed a nuclear apocalypse that covers the world in polluted darkness for all but a few hours a day, humans have turned on each other, vampires round up humans to live in camps, and there's even dissent among the resistance. This book changes up the relationship dynamics within the group and gives a full background of the vampires (although they turn out to be as mythologically/religiously/magically grounded as anything, in an interesting twist for a series that started out portraying vampirism as a disease to be studied scientifically). Overall a fitting conclusion to the series.