A devastating flaw during a mission forces Philip, Elizabeth, William and Gabriel to confront the depths of their patriotism… and their mortality. In Russia, in striving to be a better person, has Nina put her life on the line?

Martha must finally face the truth she has denied – and her life may never be the same. Plus, a chilling new development in William's work forces the Jennings to face the realities of what a biological war would mean.