On the mist-covered planet M5S-224, Maj. John Sheppard is miffed at Dr. Rodney McKay for leading them on a wild goose chase. McKay's readings had shown massive amounts of energy here, indicating an advanced civilization, but there's nobody home. As they prepare to return to Atlantis, McKay notices a wild fluctuation in the energy field of the planet's stargate. The gate is actually drawing power from this world's energy-enriched atmosphere.
That's enough energy, he says, astonished, to open a wormhole to Earth.
Back at Atlantis, McKay explains that while the Atlantis stargate is the only one with a control crystal that allows it to dial Earth, he can remove the crystal and install it in this other stargate's controller. Then that gate will be able to dial Earth, feed off the planet's energy, and open a wormhole home. But it will be a one-way trip, because the power-generating ZPM (zero-point module) back at Stargate Command isn't strong enough to reopen the wormhole back to Pegasus.
Dr. Elizabeth Weir gives McKay the go-ahead. Back at M5S 224 with Sheppard, Teyla and Lt. Aiden Ford, he opens a portal to Earth. After verifying Weir's ID code, the technician on the other end tells Weir and company to come through the 'gate anytime they're ready. Weir explains they're not ready to risk a one-way trip. But she relents when the technician says that Earth's allies the Asgard are refitting the Prometheus starship with engines capable of reaching other galaxies. If they 'gate through, they could be back in the Pegasus galaxy within a month.
Gen. George S. Hammond, the former head of Stargate Command before being promoted to head of Homeworld Security, is there to greet them. But upon hearing their preliminary report about the Wraith and the potentially catastrophic danger to Earth, he informs them that the Pentagon feels it might be best to cut their losses and abandon the Pegasus galaxy altogether. Weir is shocked and argues to continue the mission. Hammond assures Weir that her recommendation will be considered at the highest level.
The team-members go back to their homes: Weir visits her boyfriend, Simon. McKay returns to his sloppy apartment to find he has no messages on his answering machine. And Sheppard and Teyla go on a shopping spree.
But something's not quite right. Simon's kiss makes Weir feel weird. McKay gets a hot date with his gorgeous neighbor who always thought he was a creep. And Sheppard doesn't recall his bachelor pad being so big and looking like it's been furnished by The Sharper Image.
Hammond informs Weir that there has been an accident aboard the Prometheus. They can't go back to Atlantis. But McKay says they don't need the ship. And they don't need the ZPM to both establish and maintain the connection to the Pegasus galaxy, as was needed the first time they left Earth. He explains that because the gate on M5S 224 draws its energy from the atmosphere, all they have to do is establish a 3.5 microsecond connection and the planet's energy will do the rest. He just needs to run a few tests with the depleted ZPM. General Hammond thinks it's folly, but he arranges to have the ZPM brought to the lab.
Hammond tells Weir of McKay's solution and then drops a bomb on her: The situation in the Pegasus galaxy has been reassessed and it has been decided that she should be relieved of command and an all-military presence be established on Atlantis. She's also shocked to learn that Sheppard has endorsed this decision.
Weir finally realizes that this is all completely wrong. She demands that Hammond tell her what's happening. Hammond agrees she should know the truth - and he then morphs into a shimmering, energy-based entity. In the 'gate room, the entity, in Hammond's form, explains to Weir, Ford, McKay, Teyla and Sheppard - who figured this wasn't Earth when all his dead friends came over to his swinging new pad for a visit - that each of them has been living in their own illusory existence while their bodies lie on M5S-224. Teyla shared Sheppard's illusion because she doesn't have any memories of Earth. The mist that engulfs the planet is the planet's population. And every time someone comes through the gate and draws energy from the planet, many beings die. Learning from their minds their intense desire to return to Earth, this energy-based race just can't allow the team to go back to Atlantis where they might use McKay's plan that will literally drain the life out of this world.
But Weir and the rest assure the entity that they will never come back to this world and, because the entity can see what is in their minds, it knows they are sincere. They awaken on the planet surface and 'gate home - to Atlantis.