The story begins with James Allison, lying on his deathbed, reminiscing about his past lives. He believes he has lived through many incarnations, always as a member of the Aryan or Nordheimer race. Allison recalls a specific life as Niord, a powerful warrior, and his encounter with a horrific, demonic entity known as the Worm.

In his past life as Niord, he was part of a tribe of Nordheimer, wandering the world. They encounter a tribe of Picts, with whom they eventually make peace. Niord befriends a Pict named Grom and has many adventures with him, including a confrontation with a massive serpent called Satha, which Niord eventually kills.

Tragedy strikes when Niord's friend Bragi and his clan settle in the Valley of the Worm, an area feared and avoided by the Picts due to an ancient, monstrous entity. The clan is savagely massacred by the Worm, prompting Niord to seek vengeance. He uses the venom of the slain serpent Satha to poison his arrows and confronts the Worm and its bizarre, fur-covered servant in their temple. After a fierce battle, Niord mortally wounds the Worm. The temple collapses, burying the Worm and marking the end of its reign of terror. Niord, severely injured, instructs Grom to build a cairn for him in the valley to guard it eternally.