Karen McDonald has buried her past. Five years after her divorce, Karen works as a biologist studying wolves in Yellowstone National Park. But when the wolf she puts to sleep turns into a man—a man she recognizes from the recurring dreams that have haunted her for years—her rational, scientific world gives way to something stranger and more dangerous. That man is Vali, Loki's son. He was imprisoned thousands of years ago, cursed to live in the body of a wolf. Vali tells Karen that he is being hunted... and he is being hunted too. Because something has awakened beneath Yellowstone's volcanic caldera, an ancient force that could mean the end of everything unless Karen is willing to risk her life and unearth the secrets of her past to save the world. .