Ba'al travels back in time and prevents the Stargate program from being started. SG-1 must somehow restore history.
SG-1 searches for an ancient weapon which could help them defeat the Ori, and discover it may be in the Ori's own home galaxy. As the Ori prepare to send ships through to the Milky Way to attack Earth, SG-1 travels to the Ori galaxy aboard the Odyssey. The International Oversight committee have their own plans and SG-1 finds themselves in a distant galaxy fighting two powerful enemies.
An alien similar to Ra appears out of the Stargate, killing five soldiers and kidnapping another, a year after the original Stargate mission. A new team is assembled, including some old members, and they go in search of the missing soldier in order to find out how Ra could still be alive. Meanwhile, the alien Goa'uld kidnap Sha're and Skaara, implanting them with symbiotes and making them Goa'uld hosts.
