Aboard an enormous ship in space, a Stargate opens and Lt. Matthew Scott comes through. As he attempts to assess the situation, more Earth soldiers and civilians start coming through. Dr. Nicholas Rush walks over to the Gate controls and examines them. Colonel Everett Young is the last one through as flames burst out around the gate. Young puts Scott in charge before passing out from his injuries. Greer calls over Master Sergeant Tamara Johansen to tend to him. Scott then turns to one of the civilians, Eli Wallace, and asks where they are and where Rush is.
The Past: Eli Wallace
Eli is at home playing an online game and somehow ends up back at the beginning of the game. Lt. General Jack O'Neill arrives with Dr. Nicholas Rush, who says that he solved the Delara weapons puzzle in his online game, Prometheus. Rush explains that to solve the puzzle, he had to solve a millennial-old alien mathematical formula. They have a NDA for him to sign and Rush insists it'll be worth his while. Eli closes the door and goes back inside and is teleported to a ship in Earth orbit. Rush comes in and welcomes him aboard the Hammond. He explains they need his help and he doesn't know how long it'll take: they are on their way to a planet 21 light years away. Rush assures Eli that the pay for his new job will assures his mother gets the best medical coverage for her condition. If Eli doesn't accept, they'll erase his memory.
The Hammond leaves orbit and Eli watches an orientation tape made by Dr. Daniel Jackson explaining how the Stargates work. Finally he talks about how the plan is to dial the ninth chevron. Once he's done, Eli calls his mother and passes on the cover story that the Air Force has provided. He assures her that he's doing the kind of thing he always dreamed of.
Later, Eli goes to the mess hall and sits with Chloe Armstrong, an assistant to Senator Alan Armstrong of California.
Eli and Scott explore and Eli recognizes the writing from his work. They find Rush already at a viewing chamber. They realize that they're on an Ancient ship in transit. Scott asks Rush to help them get home. Johansen calls Scott to inform him that the air vents in the Gate chamber have shut down. Rush explains that the life-support system is failing and they should do something about it.
The Past: Everett Young
In his kitchen at home, Young tells his wife that he's on a new command and will be away. She's not happy at the news and thinks he's choosing her over his job, and admits she can't wait any more. He collapses…
Everett has a seizure and Johansen tries to tend to him.
The Past: Matthew Scott
On the secret planetary base, Scott is making out with a female officer as Young calls him to the bridge to inform him that the Hammond has arrived and their guests are on the way. Scott hastily dresses and runs off. They beam down and meet with Senator Armstrong and Chloe, his daughter. Eli is also there. Scott arrives and Young assigns him to Eli. They go into the base and Eli examines the Stargate while Scott explains that it's tied into the planetary power core. He notes that Eli figured out something that Rush has been working on for months, and some of the personnel are glad to see Rush shown up.
Young introduces Armstrong to the base commander, Colonel Telford. Armstrong is there to determine how the government's money is being spent. Rush explains that thanks to Wallace, they've engineered a practical solution to feed enough power to the Gate to activate the ninth chevron. Rush starts a test and the power builds up as the machinery starts to overload. They're unable to lock the ninth chevron and Young overrides Rush and has the Gate shut down. Rush insists it should have worked and Young reminds him of the danger and the priority is the safety of the base personnel. Rush puts it on Eli, much to his shock.
Rush restores power to the lights and Scott returns to tell everyone that they're on an Ancient starship. Armstrong orders him to tell them and demands to see Rush, but then starts to have heart pangs. He explains that they're running low on air and gathers two scientists to help Rush.
The Past: Dr. Nicholas Rush
Rush reviews the equations with Eli and insists that Eli's proof is the problem. Rush starts over while Young invites them to eat in the mess. Eli accepts while Rush stays behind. During the meal, Eli notes that they have no idea where the address leads or what the ninth chevron leads to. Meanwhile, Rush gives up in disgust and goes to the mess hall to get a meal. As he comes in, Chloe insists that Eli will solve it if anyone can and Rush overhears him. Armstrong proposes a toast and makes a long speech, much to his daughter's dismay.
Rush goes to his quarters and examines a photo of himself and a woman.
Armstrong continues to praise his daughter until Chloe cuts him off. They hear an explosion and then the base is rocked with impacts. Young informs them the base is under attack and gets everyone to positions, sending Eli with the Armstrongs.
Greer and the others return to the control center where Rush explains that he's trying to reset the systems. When Eli insists that he doesn't know what he's doing and points out what the screen says, Rush disagrees. Greer points his gun at Rush, angrily insisting he won't let Rush screw them up again.
The Past: Sgt. Greer
Young releases Greer from a cell, telling him that he's dropping the charges and he can take his anger out on the attackers. Colonel Samantha Carter reports from the Hammond, informing Young that the unidentified alien ships in orbit have launched gliders and opened fire on the Hammond. Some of the gliders are escorting a troop transport to the base for invasion. Telford takes a squadron of gliders up to intercept.
Rush insists he's going to push a button that will fix the life support. Greer tells him not to do it and Scott orders him to lower his weapon. Greer finally does so and Rush pushes the button. Nothing happens. Scott calls Johansen to tell her it's going to take a little more time.
The Past: Tamara Johansen
Johansen reports to Camille Wray, who wonders if Colonel Young knows. Johansen says her scholarship has come in and she hadn't made up her mind, and insists she isn't protecting anyone.
Johansen glances over at Camille, who is among the survivors.
Young and his men open fire on the incoming gliders. Base personnel register a spike in the base's power core. Rush turns to Eli and says he needs his help to open the ninth chevron before the planet's core goes critical due to the bombardment. Eli believes the ninth symbol represents the planet they're on, but they may not be on the right planet.
Telford and his men are unable to keep the troop transport from landing. Young tells his men to dial the Stargate back to Earth and gets clear of the base entry just before a glider slams into it.
The base personnel gather in the Gate chamber while Eli concludes that the ninth chevron has to be for Earth no matter what planet they're on. Rush orders the gate technician to stop dialing, warning they can't risk an open wormhole to Earth if the planet explodes. He starts dialing a new code.
An explosion brings down debris in a hallway, trapping Senator Armstrong and some of the personnel in a corridor. Johansen tends to the injured but loses one man, Simms. Young tells her that they have no choice and they have to go.
Rush dials the new address using Earth as the ninth chevron. The Stargate connects and in orbit, Carter tells Telford they can only spare two minutes before the Hammond has to retreat. Young arrives in the gate chamber and demands to know what's happening. Rush explains what happened and Young insists they could have dialed some other planet. Young tells everyone to stay in place.
Rush manages to activate the ship's navigational log. It reveals that the ship left Earth and passed beyond the Pegasus galaxy millennia ago. They are now several billion light years from Earth.
Young and Greer try to open the corridor and rescue Senator Armstrong and the others. Young orders Scott to get as many supplies as possible because they're not evacuating to Earth. Chloe refuses to leave her father.
In the Gate chamber, Scott goes through first and orders everyone to proceed every three seconds afterward. The evacuation begins as the base starts to collapse.
Young and Greer plant explosive charges and move back with Chloe. Once they blast through, they find an injured Armstrong and bring him out with the others. Young sends everyone on ahead and tries to make contact with Carter aboard the Hammond. He then heads for the Gate Chamber and grabs what supplies he can. He enters the Gate last as the planet explodes behind him, the shock wave destroying the enemy ships.
On Earth, Carter contacts General O'Neill and tells him what happened. She reports the 80 people in the bunker are MIA and O'Neill confirms that none of them beamed back to Earth. They're left to wonder where the remaining personnel went.
Scott organizes the military personnel into search teams and hands out what weapons they have. He asks Armstrong to stay with civilians and keep them calm, but Armstrong doesn't appreciate. being patronized. Unobserved by all except Johansen, Rush picks up a duffel bag and departs.