The episode name refers to the Greek legend of dragon's teeth, where the teeth of a slain dragon were sown into the battlefield. The teeth sprouted up into an army of warriors, who continued to fight.
While traveling, Voyager is caught in a subspace corridor, filled with spaceship debris nearly 900 years old. They encounter a vessel traveling in the corridor of the Turei species, who help to knock Voyager out of the corridor into normal space. When Captain Kathryn Janeway discovers they have traveled more than 200 light years in a few minutes, she requests that the Turei aid them further, but the Turei insist on wiping Voyager's computers of any information regarding the corridor. When Janeway refuses, the Turei ship engages them in combat and summons reinforcements. Janeway is forced to have Voyager land on a nearby planet, shrouded in radiation that prevent the Turei from following them. The crew begins to effect repairs as the Turei maintain position in orbit.
They find the surface of the planet to appear to have been civilized, but destroyed by orbital bombardment nearly 900 years ago. Detecting lifesigns, Janeway, Lt. Tuvok, and Seven of Nine discover several stasis chambers. Seven, without waiting for Janeway's orders, wakes Gedrin, a member of the Vaadwaur species, who mourns the loss of his female companion in a nearby chamber that had failed. Recovering aboard Voyager, Gedrin explains that his race had discovered the subspace corridors, the envy of several other races that went to war to seize control of the corridors. He and hundreds of other Vaadwaur, along with their weapons and ships, entered stasis in caverns below the planet's surface, anticipating being revived five years later, but their control equipment was apparently damaged. Gedrin struggles with how much time has passed; when he encounters Neelix, a member of the Talaxian race that the Vaadwaur has known before going into stasis, Neelix recognizes the term "Vaadwaur" as an old Talaxian word meaning "foolish".
Janeway works with Gedrin to devise a plan to fight off the Turei and return to the subspace tunnels, and proceed to waken the other Vaadwaur; Commander Chakotay is reminded of a Greek myth whereby warriors would rise after the teeth of a defeated dragon were buried in the ground. Neelix, curious about his meeting with Gedrin, reviews Talaxian folklore and finds several references to the Vaadwaur, all involving an armada of ships that would appear out of nowhere and attack other species, disappearing as fast as they arrived. With Seven's Borg database, Neelix confirms that the Vaadwaur are the aggressors, using their subspace corridors to attack planets for their own, and presents this to Janeway. Meanwhile, Voyager's crew are unaware that other woken Vaadwaur have identified the ship as a means of transporting the remainder of their population to a new colony, using its powerful weapon systems to destroy any resistance. Gedrin eventually discovers this, and warns Janeway, more intent on helping the Voyager crew than his own people.
Janeway attempts to continue to play her plans for attacking the Turei by limiting the number of Vaadwaur ships to be activated; this causes the Vaadwaur to turn on Voyager. Janeway contacts the Turei, and convinces them to help fight off the Vaadwaur. Tuvok and Gedrin return to the planet to override the signal of a satellite, allowing the Turei to use it to lock onto the Vaadwaur ships. Gedrin remains behind to assure the satellite signal remains strong while Tuvok returns to the ship; Gedrin is killed when the chamber he is in collapses.
As the Turei engage the Vaadwaur, Voyager is able to escape and leave the sector. They detect that 53 Vaadwaur ships were able to escape the Turei assault, and believe they have not seen the last of the species. Seven apologizes for her actions, as by waking Gedrin she had started a chain of events that led to a new full-scale war in the sector, but Janeway notes she may have done the same.