The SGC is contacted through the Stargate by the Eurondans, who send three volunteers through the Stargate before we can decipher their message and warn them about our iris. Alar, the leader of the Eurondans, tell the SGC of a war on their planet that has been waged for many years. In a last act of desperation, Alar and the Eurondans, who recently unearthed the Stargate and Earth's coordinates, beg the SGC for help. Hammond allows a mission on a strictly humanitarian and diplomatic mission. Hopeful for advanced technologies, Hammond authorizes Jack to negotiate trade.
SG-1 travels to Euronda and find themselves in an underground bunker, with Alar lying injured near the gate, the ground shaking from bombs on the surface. Alar is given an injection that seems to cure him of his injuries. Alar shows SG-1 a huge cryogenic facility, housing thousands of people in stasis.
Alar then shows SG-1 their national defense room. The room houses many machines where pilots can man aerial drones to attack the enemy and defend against bombers. Alar tells SG-1 that the surface of the planet has been poisoned and is no longer habitable. The Eurondons tell SG-1 that there is an unmanned drone approaching Euronda, and they offer a demonstration. Jack steps into the machine and is shown a virtual 3D image of what the drone he is piloting sees, and is told that the machine works by thought control. After destroying the drone, Jack sees another pilot in bad condition, and is told that with prolonged use, the machines cause permanent neural damage.
Alar tells Sam that they utilize controlled fusion reactions, fueled by heavy water. Jack tells Alar that Earth can provide the heavy water they require, in exchange Alar offers everything that Euronda has worth trading. Daniel has reservations about this deal, as it would lead to the Eurondans attacking their enemy, instead of fleeing through the Stargate to another planet. Another bombing run ensues, and Jack goes to help defend the Eurondans.
Daniel and Sam return to Earth, with Daniel giving heated protest. General Hammond, hearing Sam's descriptions of the Eurondan technology immediately allows the trade of heavy water. Daniel makes the point that we don't even know why they're fighting.
Teal'c and Jack help fight off their enemy using the attack drones, while Sam and Daniel return with a supply of heavy water, as much as the SGC could procure on short notice. The Eurondans use the fuel to power their defense shields. Teal'c and Jack shoot down two enemy bombers, and were shocked to find that they were not unmanned like the drone Jack shot down earlier. Alar tells Sam that the fuel provided will only fuel their defense field for several hours, Sam promising that the SGC will provide more fuel in time.
After the battle, the Eurondans hold formal negotiations with SG-1. Daniel asks how the war started. Alar explains how the enemy bombed first in a surprise attack. O'Neill agrees to the terms of trade.
Alar asks later that Teal'c not return, because he is, "not like us". Daniel prepare to head back to Earth, but Jack pulls Daniel back to ask questions to uncover the truth about the Eurondans, disturbed by Alar's comments. Sam realizes that the bunker must have been built before the war was started. Sam is given access to a schematic of the bunker, and she looks over the details with great scrutiny.
Jack and Teal'c break into the Eurondan cryo facility and discover that of the thousands of people frozen, that they are all of only a few base copies.
Daniel asks Alar's assistant what the Eurondans call their enemy. She tells Daniel that they call them Breeders, that they reproduce without regard for genetic purity, that they are of all races.
Sam asks Alar about pipes leading to the surface, and Alar confesses that it was the Eurondans that poisoned the air. During the confession another bombing run ensues and Jack tells Alar that the fuel supply will be delayed. Jack offers himself and Teal'c as pilots. Learning of the Eurondans genocide, Daniel tells Alar that they will not receive any more heavy water. Jack and Teal'c escort the bombers allowing them to bomb directly above the bombers. Jack then crashes the drones into the surface. SG-1 escapes to Earth as the Eurondan bunker is destroyed.