After being chased by creatures and visiting an ice planet, the team begins to wonder if they are on a pointless quest. Draga opens a gate to ""where they wish to go"" and they end up on Earth in the Yucatan, where a local professor working for a Horace Van Gelder reveals she discovered the new gate. The shapeshifter Nephestus, disguised as Grimes, is working with Van Gelder and gets word the team is present when they contact Stargate Command. Disguised as Stoneman, Nephestus welcomes them and claims he'll help them clear their names, then summons Da'kyll and his Tlak'khan. Draga suspects something as Stoneman sends the cadets into Cancun â€“ in fact it's an ambush but they turn around and return. Gus and Draga catch on and make their escape while the others return in just in time to rescue them. The team is forced to escape through the Gate and go on the run once more before they can clear their names, and the Tlak'khan and Nephestus depart with Van Gelder as Nephestus takes his place to
The team arrives on a planet and helps the native Ner'alds against a energized dragon-creature, a late arriving Harrison manages to knock it out. Stacey and Seattle admire the locals' markings and the guys end up teasing Stacey into getting a marking. It turns out that the paint is made of microbes and they start spreading on Stacey. They're not toxic, but will cover her entire body. They need a stream with mud to make a removal salve but another energy-resistant creature attacks â€“ Gus takes Stacey while the others hold off the monster. Avoiding a variety of dangers, Gus and Stacey make it just in time but the stream has dried up. A persistent bug creature that has been following them finally latches on to Stacey and sucks off the microbe.
The team arrive on a desert planet in the middle of a sandstorm and meet Mashuma of the Mo'Tai people and his tribe. Seattle leads the group in helping the Mo'Tai find buried water and then finds an irradiated rock that could be used to power the pumps but Seattle soon becomes impatient to help and uses full power, setting off a quake but finding a huge energy rock and a energy sphere that unleashes memories for Seattle of how her father refused to admit his mistake in moving away from their home to the city. Seattle continues and is injured during an excavation but is more determined then ever. Another energy sphere escapes and heads for the village and Ec'co figures out how to trap it long enough for Draga to establish communication with the creature and determine its want to return home to the energy-rocks. Without the rocks, the team comes up with a way to use windmills to run the pumps.
After escaping the Tlak'khan on a jungle world thanks to Harrison's flying skills (sort of), the team arrives on a sulphur-covered planet and bat-like inhabitants, the Har'un. With his jetpack damaged Harrison accepts an invitation to fly with the locals but doesn't do so well. Determined, Harrison keeps trying but is the only one in the group who can't manage. The planet is polluted due to the Tlak'khan's efforts and they send a team to attack – Harrison has to mount up to warn the others and manages to get the hang of it. the Tlak'khan refuse to learn from their mistakes and fall victim to the Har'un's gas bombs.
The team find themselves on a plant of locals who worship and emulate the Tlak'khan but are suffering from a plague. Draga cures as many as she can but the leader, Mek'rod, insists they are the Tlak'khan and follow their ways, but eventually acknowledges the Tlak'khan merely provide them with help. Ec'co comes up with a cure for the plague while the Mar'dan elders summon Da'kyll and his men who tell the Mar'dan to obey them and lure the team into a trap. The Tlak'khan abandon the Mar'dan to the plague and Mek'rod turns against them. The team breaks free only to enter a trap, but the Mar'dan turn against the Tlak'khan and drive them off.
The team arrive on a resort-type planet where the locals are obsessed with fashion accessories to the point of endangering themselves. They befriend Rikell and the women and Harrison help her to gather some ferns to make a fashion statement and run afoul of the local wildlife, while a mercenary attacks the team up above and grabs Draga. The others get clear with Harrison's scientific knowledge and catch up to rescue Draga. The team gets enough of the ferns from the merchant that helped out the mercenary to let Rikell make an outfit but she realizes she doesn't need a fancy outfit.
The team arrive on Octasar where a Dr. Carrie Mason of the SGC is working with a local scientist, Dr. Bri'sal, who is working on a project of universal telepathy as part of a scientific conference and believes the Tlak'khan can help him – they're playing him, naturally, since Bri'sal's fellow scientists don't support his project. Stacey overhears them while the rest of the team convinces Mason they're not traitors. Mason doesn't believe them and when the project succeeds the Tlak'khan take control. The team launches an attack but the mind-controlled scientists are forced to attack them, but Mason grabs Da'kyll's device, freeing everyone and forcing the Tlak'khan to retreat.
The gang find a mysterious ship emitting dangerous energy on an uninhabited planet. While Harrison and Seattle look for the owners the others break into the ship, much to Stacey's concern. Gus insists on using the ship to return to nearby Earth, unaware that it's actually a Tlak'khan trap – the ship takes them to Ga'Harn, the Tlak'khan homeworld. Da'kyll captures them all and holds them back from the Nax'kan Council by claiming Warrior Right of Capture. Hah'lak sends his own operative, Gal'korn, to free first Gus and then the rest of the SG team and they see through the deception. They get their vehicles and weapons and get to the nearest Stargate to make their escape.
The team arrives on a civilized high-tech planet, Rokari, where they determine a comet is heading for the world they're on with only 60 hours to spare. The local government, the Commonality, don't believe their warning and state they have outgrown written and recorded language. The team break out a member of an underground resistance that distributes writing and leads them to a hidden library with info on how to use the planet's defense system. Harrison manages to figure out the language and the team activates the defense system, the Commonality sees the value of writing and everything turns out well.
The team arrives on an ice planet and intervenes in a fight between the Tlak'khan and the native Ursons. They win the day for the natives but begin to suspect all isn't as it seems. Seattle follows a young Tlak'khan to a hidden city while Gus interrogates the prisoners who it turns out are farmer/refugees. The team realizes the Ursons are in the wrong and turn against them to help the Tlak'khan farmers.