The Queen of Hel (The Norsewomen, #5)

Norway, AD 824. The evil Queen in the Mound is dead, the Irish necklace held fast in her ghoulish grip. Undisturbed, the queen’s curse lies dormant. But Ragnhild attempts to retrieve the necklace, unleashing a pestilence on Tromøy. As her people sicken and die, Asa must seek the cure in the Otherworld. Leaving her beloved son behind, she travels alone to the dark world deep underground, a place from which mortals never return. The realm of Hel herself.