SG-1 is preparing to leave for a mission when General Landry pulls the plug. A team from the International Oversight Advisory is going on a tour of the Gamma site and SG-1 is ordered to escort them.
The IOA team arrives at the SGC and introductions are made after which they step through the gate. While touring the base at the Gamma site Carter explains that this planet was chosen for several reasons including the fact that the ionosphere makes targeting from space difficult, a desirable trait to help to avoid having the Stargate stolen. They meet Dr. Meyers who shows them some bugs designated R-75 which is suspected of being a new weapon that Priors use, one to wipe out crops. He explains that the bugs had a very short life span until their food was withheld. The bugs are also more active in the dark, subterranean by nature, and use echo-location. The tour continues while Mitchell and Daniel debate the IOA's presence.
Dr. Meyers tries to feed the bugs a leaf but they completely ignore it. He then drops a piece of his meat loaf into the tank which causes flurry of activity as the bugs swarm on it.
At the commissary Daniel talks with Shen Xiaoyi—the former attaché to the Chinese mission in the United States—about America's grip on the Stargate program. Dr. Meyers and Dr. Pullman return to the lab to find the tank that formerly contained about a dozen R-75 is now packed with them. As they look on, the rapidly-reproducing bugs shatter the glass and escape into the lab. The doctors initiate emergency procedures to seal the door and suck the bugs into bio-hazard disposal chutes. Once the lab is cleared they open the door but not before Meyers is bitten by one last bug.
The tour is completed and the IOA team heads toward the gate room. They run into Meyers who collapses in front of them. Pullman explains that Meyers was bitten but cleared by medical. But now R-75 has changed when they ate the meat loaf and is now carnivorous. Agent Woolsey says that the IOA team is getting nervous and wants to return to Earth, but the base is now locked down until the cause for Meyers' illness can be found. Meyers is prepared to be returned to Earth for examination in a quarantine container but bugs come out of Dr. Meyers' mouth and the airmen drop the cylinder. Everyone flees to a higher level as the base is locked down.
Sam theorizes that the bugs laid their eggs in Meyers when he was bitten and that the Priors designed them; either the bugs destroy crops or they adapt to eat flesh. The power goes out and communications become erratic. The base commander, Colonel Pearson, tells the IOA team that they'll be escorted to the surface and Woolsey demands that SG-1 escort them. SG-1 lead the IOA through the forest to a research station five miles away when bugs emerge from the ground and completely devour one of the airmen. They retreat to a rocky cave where the bugs can't burrow through. Carter states that the bugs are sensitive to sound – shooting at the ground drives them back.
On Earth, General Landry learns of the dire situation at the Gamma site and authorizes a neuro-toxin to be deployed on the planet to wipe out the bugs. The toxin is lethal to humans as well but Landry believes that they are all dead already.
While waiting in the cave, Shen Xiaoyi confides in Daniel that her report is just a formality and that it will have no bearing on her government's decisions about the Stargate program. She asks him whether he would still have accepted the offer to join the Stargate program if it had come from China instead of the American military and he confirms that he would have. Mitchell cannot contact the Gamma site at all. He tries to comfort Airman Walker who later scratches at his neck, where a bulge moves beneath the skin.
The next morning SG-1 concludes everyone at the Gamma site is dead and their only hope is to get to the F-302s. Daniel runs in exclaiming that Walker is missing and he, Mitchell, and Teal'c go look for him. They find Walker lying in the forest and attempt to wake him. Walker trembles and explodes in a mountain of bugs. Mitchell orders them to stand still and the bugs, unable to detect them, retreat into the ground. Cameron and Teal'c leave to get some F-302s in the hopes of picking up the rest of their party and taking them across the planet, while Daniel heads back to the cave.
As they walk, Mitchell talks with Teal'c about hope and confidence. They also discuss what movie Teal'c wants to watch tomorrow night. Everyone feels a large explosion and Mitchell reports that the base's self-destruct has been triggered. The Gamma site has been destroyed. Back in the cave, Mr. Lapierre is panicking and Woolsey warns Carter that the fate of Stargate program lies with the IOA and that their survival would help minimize the fallout from what was supposed to be an uneventful tour.
While Mitchell and Teal'c are walking back to the cave they make conversation about Teal'c establishing a home for himself off-base. The ground suddenly rumbles with bugs beneath their feet and lasts a few moments. Daniel radios them and the ground rumbles again. Several seconds later they continue walking very slowly to avoid giving away their location.
At SGC, Sgt. Harriman informs Landry that the Odyssey will arrive at the Gamma site in five hours.
Mitchell and Teal'c return to the cave. Carter reveals to everyone the protocol that the SGC will likely enact. She explains about the neuro-toxin and how they will be unable to signal the Odyssey because their transmitters won't work due to the interference from the atmosphere. Worse still, their lifesigns will be lost amidst the lifesigns of all the bugs. Daniel suggests that they can send a signal to the Odyssey from the research station if they can get there.
SG-1 and the IOA team begin their trek through the forest but Lapierre is having difficulty keeping up. He insists on taking a break but Mitchell scares him into action. The Odyssey gets closer.
As they near the research station Shen Xiaoyi twists her ankle and the bugs close in. Carter and the IOA team enter the station while the others fire into the ground. Sam warns that the vibrations from the communications array are attracting the bugs and Mitchell tells her to hurry because they're running out of ammo. They plant explosives around the station to drive them off. Carter finishes patching into the comm-array but the signal will not be detected until the Odyssey enters orbit—of course they have no way of knowing when that will be.
Sam joins the rest of SG-1 and they wait as the mines go off, but the bugs retreat for only a few seconds. The bugs drive SG-1 further and further back. Just as they run out of their last rounds of ammunition and all hope is lost, they are all beamed off the planet.
At the SGC, Woolsey briefs General Landry and SG-1 on the other delegates' status. He tells them that the IOA understands that what happened was not SGC's fault and the SG teams are greatly appreciated. After he leaves, Landry tells SG-1 that two more planets have been attacked with the bugs and that R&D is working on a safer defense that will harm only the bugs. SG-1 then heads off and discusses what movie to watch.