The Tok'ra have captured Ba'al and are about to perform a ceremony to remove his symbiote. However, it's not him but the last of his clones.
The real Ba'al has travelled back in time to earth where he attacks the ship which is transporting the Stargate to the USA. Because of this alternate timeline, the Stargate programme was never created
SG-1 gate back to Earth and find themselves abroad the derelict Achilles now stuck in the frozen arctic. Though they are rescued, Daniel pays a heavy price and the airforce refuse to let them do anything to change the timeline.
A year later Ba'al and his attack fleet threaten the earth, is there still a way SG-1 can save the planet?