While SG-1 attends the execution of Ba'al, the last of the Goa'uld System Lords, Teal'c and Vala inexplicably disappear into thin air. Carter, Daniel and Mitchell race back to Earth, only to emerge from the gate inside the hold of a derelict WWII ship lodged in the Artic ice. They soon realize that Ba'al must have gone back in time and captured the ship that was to bring the Stargate to America, thereby erasing the Stargate program from history. As they try to convince the authorities that they must find a way to set things right, a fleet of Goa'uld motherships arrives in orbit, led by Ba'al, his queen, Katesh (Vala), and his first prime, Teal'c. SG-1 must get to the Stargate and find a way to return the timeline back to normal, otherwise the world will be divided up among the Goa'uld System Lords, and enslaved forever.

SG-1 travel to the ruins of Dakara in hopes of finding the fabled Ark of Truth. Built millions of years before, this Ancient artifact may be the only means remaining to defeat the Ori armies who have thus far proven unstoppable in their quest to conquer the universe in the name of their religion, Origin. Upon learning more Ori ships are about to be sent through the Supergate to launch a final assault on Earth, Daniel discovers that the Ark of Truth, may actually be in the Ori home galaxy. With Mitchell reluctantly in command of the battle cruiser the USS Odyssey and the IOC over-seeing the mission, the SG-1 team make their way to a distant galaxy – and the heartland of the Ori forces. But what they find there will challenge them all in ways they could never have imagined.

The SG-1 team extends a small time frame to several years to survive an attack of the Ori and tries to find a solution to solve their problem.

SG-1 gets caught in the middle when Ba'al and Adria compete for domination of the galaxy.

Vala's father Jacek contacts SGC claiming to have vital information that could impact the survival of Earth. Meanwhile, Gen. Landry's ex-wife pays a visit.

After a terrorist attack on a Jaffa summit leaves many dead and Bra'tac seriously injured, Teal'c goes on a one-man quest for revenge.

SG-1 finds an alien museum on another planet but are mistaken for a bunch of rebels that have taken hostages.

Col. Mitchell returns to Kansas to attend his high school reunion with Vala when Stargate Command learns of an attack on SG-1 team members.

The SG-1 team learns of yet another world that has been visited by a Prior of the Ori. However, this Prior hasn't issued any threats. The team waits for the Prior's return, only to be shocked by his identity.

Carter ends up in an alternate universe and changes the course of things in that universe.

Mitchell, Carter and Teal'c arrive on a planet being threatened by the Ori. They decide that a line needs to be drawn and that the Ori must not be allowed to advance any further. Carter attempts to use the Ancient Merlin's technology to prevent the Ori from taking over the planet.

SG-1, Adria, and Ba'al must defeat the dragon and continue their quest to search for Merlin's weapon.

This special deals with how the SG-1 series intertwined many of Earth's mythologies into its plots and story lines, and about the many alien character connections with Earth's great mythological figures.

The SG-1 team continues their quest for the Holy Grail, an Ancient device capable of killing the ascended Ori. They learn that an old nemesis is also looking for the device.

Mitchell attempts to infiltrate the Lucian Alliance in order to rescue members of the SG-1 team from the fallout of an Alliance civil war.

Vala finds herself alone in a city with no memory of her identity or past life. Meanwhile, Mitchell and Teal'c question a man named Weaver who may have information about Vala's whereabouts.

After Adria's followers on a planet are wiped out, she attempts to learn the location of this powerful new weapon.

Mitchell eagerly awaits the next off-world mission, which will be his 200th trip through the Stargate. However, Martin Lloyd returns and seeks help with his movie script. The Pentagon (and General Jack O'Neill specifically) orders SG-1 to assist, much to SG-1's chagrin.

The 200th episode of the venerated sci-fi series is discussed during this special. Also, interviews with cast and crew reminisce about the entire series.

While assisting SG-3 on an offworld mission, Teal'c encounters a savage alien creature that is killing the inhabitants. SG-1 investigates and learns that a parasite is to blame. The team suspects that the Ori are responsible, but they are shocked when they find out the real cause.

Stargate Command faces off against their old nemesis Ba'al and his clones as Landry spars with the NID and Agent Barrett.

Daniel and Vala travel to Atlantis in search of Merlin's anti-Ori weapon, while Sam and Mitchell join forces with Dr. McKay to lock out the Ori supergate.

The team goes off-world seeking a weapon against the Ori and ends up in serious trouble. Meanwhile, Landry is faced with having to decide whether or not Vala can be trusted to remain at the SGC.

As the Ori gain power with their invasion of Chulak, Vala's daughter Adria ages years in a matter of hours and the secret of her conception is revealed.

Amanda Tapping takes us on a fascinating look at how many aspects surrounding SG-1 have a basis in real science.