A ruinous war or series of wars has devastated the Terran Federation. As a result, the technologically less advanced Sword Worlds are able to send their starships raiding and pillaging (hence the title of H. Beam Piper's 1963 novel).
Baron Lucas Trask of the Sword World Gram is about to marry his beloved Elaine when demented suitor Andray Dunnan crashes the wedding and kills her and wounds Trask. He then steals his uncle's new starship. When Trask recovers, he pledges his barony in exchange for a starship, the twin of the one Dunnan stole, so he can hunt for the murderer, no matter how small the chances are of tracking him down in the vastness of the galaxy.
Trask eventually establishes a base on Tanith, a primitive, though human-inhabited planet, then goes raiding himself. He sees more profit in interstellar trading than raiding, and also begins training the people of his new planet. People begin emigrating from Gram to Tanith to take advantage of the burgeoning opportunities.
Finally, Trask learns that Dunnan is behind a plot to take over Marduk, a democratic, advanced planet. He gathers his allies and arrives in time to put down the coup and execute Dunnan. By this point, however, dealing with Dunnan has become less important to him than building a civilization on Tanith.
Best part of story, including ending:
It's a twist on the old theme of empire building.
Best scene in story:
During one of his early raids, Trask comes upon a man holding the body of his dead wife, a casualty of the raid. He shoots the man and wishes that someone had done the same to him after Elaine was killed. It is ironic that he has inflicted the same pain as Dunnan.
Opinion about the main character:
Trask changes from a vengeance-obsessed man to a builder.