St. Brice's Day, England, Anno 1002. At the order of King Aethelred, thousands of Danes are murdered in a frenzy of ethnic cleansing. Outraged, the Danish king, Sweyn Forkbeard, swears he will take Aethelred's head, and his crown.

But Sweyn needs allies. Chief amongst his supporters is Aelfgifu, an English noblewoman and head of a once great family. She has her own reasons to hate Aethelred and as a pagan, she is sympathetic to the Danish cause. When Aelfgifu marries Sweyn's son, Canute, war is inevitable.

But if Aethelred is weak, Emma, his Norman queen, is not. And she will stop at nothing to destroy the woman at the heart of the Viking army.