As the team embarks upon its tenth year, Vala, a former Goa'uld host turned freedom-fighter, joins SG-1 in their battle to defend the galaxy from the holy war of the Ori. Having discovered the existence of a weapon capable of defeating the Ori, the team is now in a race against time to find it before more systems fall to the influence of the Priors and the threat of the newly arrived Origin fleet.
The season is continued with direct-to-DVD film Stargate: The Ark of Truth.
As the Ori invade the Jaffa planet Chulak, Vala and Daniel must deal with their leader: Vala's young daughter, rapidly aged by the Ori to serve their purposes.
SG-1 investigates a problem off-world and soon finds that they have become victims themselves: they cannot stay awake. Meanwhile, Vala Mal Doran undergoes an evaluation on Earth, hoping to join SG-1.
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.
When Baal comes to Earth seeking help, Stargate Command must capture his clones and determine which one is the genuine article.
Teal'c discovers a world where people are being savagely attacked by an elusive creature, leading SG-1 to a stunning discovery about its potential origin.
Martin Lloyd seeks out SG-1 for assistance when his failed TV show based on the real Stargate program becomes a feature film.
The Jaffa take the fight to the Ori, using a genocidal weapon on their new worshipers and landing SG-1 in the middle of a war they can't control.
Striken with amnesia and on the run, Vala takes a job as a waitress as she tries to piece together who she is and what happened to her.
Cameron Mitchell must go undercover inside the deadly Lucian Alliance to prevent his teammates from becoming casualties of an Alliance civil war.
SG-1 races against Baal in the hunt to find the Sangraal, Merlin's anti-Ori weapon, and comes up against a series of ancient trials.
When the team finds Merlin himself, they must help him complete the Sangraal weapon before Adria and her Ori forces can track them down.
SG-1 tries to defend a planet from the Ori by hiding its people in another dimension. Vala attempts to convince her husband Tomin of the Ori's true motives.
An experiment gone wrong pulls Samantha Carter into a parallel reality, where she must save Earth from an Ori assault before she will be allowed to return home.
When SG-1 discovers that Daniel Jackson has been turned into a Prior of the Ori, they must determine whether or not his plan to destroy the Ori is genuine.
When the Lucian Alliance puts a bounty on SG-1's heads, Cameron Mitchell finds himself a target while attending his high school reunion.
SG-1 realizes they have stepped through the gate into another planet's museum -- but are mistaken for a band of zealous rebels who have taken hostages.
When a terrorist attack decimates a Jaffa summit Teal'c strikes out on a quest for revenge, believing that the perpetrator is one of his own pupils.
Earth provides sanctuary for Vala's estranged, con artist father after he provides intel about a Jaffa plot to attack the planet.
SG-1 hatches an elaborate plan to try and capture Adria, using Vala as bait.