Orcus is locked away in a magical dungeon by Ominor and Wood, his most powerful wizard (who goes on to become the main antagonist of the subsequent Swords series set thousands of years further in the future).
On one continent, a resistance movement fights on under the leadership of Duncan, but is gradually being ground down by the greatly superior military and magical strength of the Empire.
Rolf, a peasant farmer with an untapped knack for technology, joins the resistance after his parents are killed and his sister kidnapped by soldiers of the Empire.
He is contacted by Ardneh (made sentient by The Change and the actual leader of the West), who uses Rolf's technological talents to effect repairs to and enhancements of itself.
Written in the 1960s and 70s, the books have a significant Cold War theme and the parallels between the American perspective of the evil east and the west are obvious.
The dominance of magic makes for a strong fantasy flavor, but remnants of the advanced weapons and technology of the old world appear throughout the series (the lake of life for wounded soldiers for example).
The first three books are tightly connected, dealing with the West's struggle to bring down the Empire, in which Rolf plays a vital role.