Two years after their adventures in The Land of the Silver Apples, the apprentice bard Jack and his Viking companion Thorgil confront the malevolent spirit of a vengeful mermaid and begin a quest that casts them among the fin folk of Notland.

After Jack becomes apprenticed to a Druid bard, he and his little sister Lucy are captured by Viking Berserkers and taken to the home of King Ivar the Boneless and his half-troll queen, leading Jack to undertake a vital quest to Jotunheim, home of the trolls.