Part 1 - Gram

On the Sword World Gram, Lucas Trask, Baron of Traskon, is about to marry Elaine Karvall, whose father owns the Karvall steel mills. In addition to being a political alliance, it is also a love match. But Andray Dunnan, the insane nephew of Duke Angus of Wardshaven, is under the delusion that Elaine loves him and is being forced into the marriage. When she tries to correct him, his anger boils over. He crashes the wedding ceremony, kills her and seriously wounds Trask, before stealing the Duke's newly built starship, the Enterprise, and escaping.

When Trask recovers from his injuries, he pledges the Barony of Traskon to Duke Angus in return for another warship, twin to the one hijacked by Dunnan. He hires Otto Harkaman, an experienced Space Viking captain who had lost his own ship in a civil war on Durendal, to command the new vessel, which Trask christens Nemesis. Trask sets out in search of Dunnan, though Harkaman warns him that given the vastness of the galaxy and the speed of spacecraft, his goal is nearly hopeless.

Part 2 - Tanith

They first visit Tanith, a primitive planet Duke Angus had planned to turn into a raiding and repair base. They find two run-down Space Viking ships already in possession, the Lamia and the Space Scourge. Trask decides to implement the Duke's original plan, taking in the other two crews as very junior partners. The natives begin receiving better treatment at his hands and training in the use of modern technology.

After some refitting, the Nemesis and the Space Scourge raid three planets, Khepera, Amaterasu and Beowulf. The loot Trask sends to Gram excites interest (and greed). Duke Angus uses the incentive of shares in the Tanith venture to gain supporters and assumes control of Gram. He promotes himself to king and names Trask his viceroy on Tanith with the rank of prince. Ambitious men begin emigrating to Trask's new realm.

Beowulf is the most advanced of the raided worlds, lacking only interstellar space flight. Puzzled, Trask investigates and finds out that it has no gadolinium, an essential element for hyperdrive engines, but does have plutonium. Coincidentally, Amaterasu (another world rising back up after undergoing decivilization) has sizable deposits of gadolinium, but lacks plutonium. Trask seizes the opportunity to set up profitable, peaceful trade between the three planets. In the process, he gradually gains two allies.

Meanwhile, ships that put into Tanith for trade and repairs occasionally bring news of sightings of Dunnan. From what he learns, Trask wonders if his enemy is plotting to conquer the civilized world of Marduk, a feat thought impossible — just the thing a megalomaniac like Dunnan would attempt.

He visits two Mardukan colonies, finding that Dunnan had recently attacked them. At the third, he comes upon the Enterprise and another Dunnan ship locked in combat with the Royal Mardukan Navy warship Victrix. He jumps into the fray and destroys both enemy ships, though he remains unsure if Dunnan was killed. The Victrix, under the command of Prince Simon Bentrik, is too badly damaged for hyperspace flight, so Trask takes the crew back to Marduk.

Part 3 - Marduk

Trask becomes friends with the Mardukan royal family and particularly King Mykhail, the constitutional monarch of Marduk, but is contemptuous of their shaky democracy. It appears that a fanatical rabble-rouser named Zaspar Makann is poised to win the next election and become Chancellor, but that is not Trask's concern. He does, however, pursue a romance with Lady Valerie, a Mardukan noblewoman who is lady-in-waiting to King Mykhail's eight-year-old granddaughter

On Gram, King Angus has been abusing his power, straining relations with the other powerful nobles and also with Trask. Finally, Prince Trask declares Tanith's independence and renounces his fealty to Angus. Later, word reaches him that civil war has erupted on Gram. Many of Trask's followers urge him to claim the throne himself. Lucas is not interested. Gram, along with the other Sword Worlds, is in decline; Tanith is the future, the core around which civilization might possibly reform. To distract his divided subordinates, he fabricates a more immediate threat, claiming (without proof) that Andray Dunnan is responsible for the unrest on Marduk.

His big lie turns out to be the truth. Not winning a majority in the election, Makann seizes control of the government. Prince Simon Bentrik shows up on Tanith as a refugee with the royal granddaughter and the lady-in-waiting Trask fancies. Prince Simon brings two pieces of news: fighting has broken out on Marduk; and, more important, that Andray Dunnan is the power behind Makann.

Trask assembles a fleet of ships, including independent Space Viking ships, the raiders of Tanith's Navy, and loyalist Royal Mardukan Navy ships and speeds to Marduk for the final showdown. He wins a fierce space battle in orbit above Marduk and his fleet lands on the surface to take back the planet. Space Viking and loyalist ground forces root out Dunnan's followers. Some of the last holdouts surrender, handing over Andrey Dunnan in return for their lives. When the insane Dunnan raves that Elaine is waiting for him back on Gram, Trask shoots him dead in an act he sees as having no more importance than shooting a mad dog.

Prince Lucas decides to marry Lady Valerie if she will have him, and take the title of King of Tanith. He also decides to strive to form a League of Civilized Worlds out of the alliance that rescued Marduk.