Having arrived through the stargate via puddle jumper, Sheppard, McKay, Teyla and Ronon set out to explore an unfamiliar, overgrown island. There, they discover a village that seems to have been abandoned only moments before.
Turns out, it's a trap: The villagers attack with primitive weapons and incredible ferocity. Outnumbered, Sheppard orders his team back to the puddle jumper. Even this retreat seems nearly impossible until a high-tech ship descends from above and drives off the islanders. Grateful for the rescue, Sheppard allows this mysterious new arrival to escort him and his team to safety on the planet's mainland.
There, they discover an advanced culture, complete with a gleaming city and an experimental power system that McKay is instantly itching to tinker with. The team meets with the planet's Magistrate, who is excited by the rare chance to trade with another advanced culture.
When the Magistrate announces that the Wraith always leave his people alone, however, Sheppard's team gets suspicious: The Wraith never leave advanced human cultures alone. The Magistrate then elaborates that his world's worst criminals are sent to the island, where the Wraith can come through the 'gate and feed without molesting the rest of the planet. Unnerved by this unique form of capital punishment, the team nonetheless prepares to return to Atlantis and escort Dr. Weir back to begin treaty negotiations.
As Sheppard pilots the puddle jumper toward the 'gate, however, the dangerously inventive islanders - led by their mastermind, Torrell - manage to shoot down the jumper. They take Sheppard and his team captive and force McKay to begin repairing the jumper for their own escape.
Concerned by the team's disappearance, Weir deploys a second jumper to investigate. She goes along to meet personally with the Magistrate. When she does, she learns that his deal with the Wraith is deeper and more disturbing than anyone - including his own people - ever knew.
Meanwhile, trapped on the penal island, Sheppard's team struggles to escape their devious captors. They have to work quickly, because the Wraith are hungry, and another culling is expected to begin at any moment....