The Ancient database on Atlantis lists the planet Doranda as the home of a great people, but when Sheppard and his team arrive they find nothing but a decimated, lifeless Wraith fleet in orbit and 10,000-year-old rubble on the planet. Only one structure survives intact.
The team lands and explores this mysterious building, where McKay makes an incredible discovery: It contains the most massive weapon he's ever seen, plus a generator vastly more powerful than a ZPM. Although the Ancients who built it couldn't perfect it before Doranda was destroyed by the Wraith, this could still be their greatest invention - the universe's ultimate power source.
McKay and his science team devote themselves to this new project. Soon, McKay claims that he's ready to fire up the generator. For a few moments, the test seems to succeed - then catastrophe strikes. The power levels spike unpredictably, and a massive surge of radiation kills a member of McKay's team. Weir orders McKay to abandon the experiment.
Meanwhile, Teyla and Ronon are on a different mission, bartering for grain with the Belkan people. With his blunt reliance on force, Ronon proves to be a troublesome partner in the delicate negotiations. Then he discovers that there are survivors from his homeworld living among the Belkans.
Having believed for years that he was the only survivor of the Wraith attack on his world, Ronon spends an emotional night drinking with an old military comrade. The next day, he learns that his old mentor, Kell, is visiting the planet. Ronon insists that Teyla set up a meeting with the man, so she does - but as soon as Kell enters the room, Ronon kills him. Shocked at this violence, Teyla feels almost as betrayed as the dead man.
Back in Atlantis, McKay is obsessed with making the Ancient generator work properly. Although Weir doubts that he can succeed where the Ancients failed, she decides to trust him enough to risk a second test.
But once again, catastrophe strikes. The weapon overloads, and McKay can't shut it down. It turns out that this weapon, not the Wraith, is what killed the Dorandans - and this time it's going to destroy half the solar system, as well. Unless Sheppard can fly them to safety, McKay is going to pay for his arrogance with his life.