In Return of the Black Swan, we begin to see the fabric of the Viking Age fray. Olav Haraldsson returns to a war-weary Norway to proclaim himself king, and no one has the power to stop him. Meanwhile, Prince Canute inherits the crown of England, even as the deposed King Ethelred and his forces rally for a counterattack. Thorkell the Tall tries to win back Canute's favor and is given a mission that will test his loyalties.

Hilja embarks on a new voyage to deliver two of the Witch's children back home from Lapland, but their mission is fraught with mishap and danger. Paavo's father Veli attempts a difficult overland trek to Inari at the onset of winter to bring back Elsa's sister in time for the birth of his grandchild, as Kokolu reels from a crone's bitter curse. In Vestfold, the Witch's daughters discover that they have been chosen as the new Norns, the Weavers of Fate, but they cannot begin to repair the world they know until they can overcome their differences.

Agatha navigates her new position as Lord of Rothskilde with more grace than she handles her pregnancy, straining her already tenuous relationship with Eleanor Locksley to the breaking point.

Norway must bow to the cross to survive into the next millennium unless the Norns can find a way to weave the threads of Fate in the Gods' favor.