In this last book of Mordec's adventures, he goes to war as a soldier in the Viking army.

In alliance with English forces, the Vikings engage the Army of the Redeemed, which, under the leadership of Abbot Alonso de Llama, aims to conquer the British Isles and expel the Vikings from England. The Abbot holds Mordec to be his personal enemy.

The Vikings are led by a famous warlord, Commander Tostig, and a great tycoon, Harald Goldmountain, the richest man of the age. Harald befriends Mordec, and treats him as his own son, having almost given up hope of finding the son he has lost.

The great battle is fought, Mordec in the thick of it. His friends, Lily the young queen and Gus the born warrior, continue to play a prominent part in the story. There is genius and foolishness in the adventures, and tragedy and comedy.

Mordec the Conqueror resolves the events of the series.