From the publisher:
This Cthulhu Dark Ages supplement focuses on magic and horror in the Viking Age. It describes the Norse world and its magic. It examines shamanistic traditions in Northern Europe and hypothesizes an Otherworld, its inhabitants, and its connections to the Cthulhu Mythos. It offers a set of spells for Investigators and their adversaries.
Then follows several linked scenarios in which the Investigators encounter the gods, spirits, and sorcerers active in the Viking world.
They discover that even the gods offer only a thin shield between humanity and a vast, uncaring, universe.