'You have seen a glimpse of this world, and once you have glimpsed it there is no going back. You will see it again and again, for that is the nature of this unseen reality. Once you are aware of it, it is aware of you.'

Katherine Kramer has been avenged. But at what cost?

Richard Kramer, still nursing his injuries, is on his way to Germany with Lily Lefèvre to find his sister Anne and her children. Charlie Bentwith is struggling to overcome the trauma of recent events and the enigmatic Dr. Westcott seems to be distracted by problems of his own.

When a new threat arises from an unexpected source, the group of friends who had been bound together by Katherine's death are scattered and still reeling from their recent ordeal.

Can they come together a second time to fight this new danger? Or will the divisions which are beginning to surface be too much to overcome?