H2 - these tv.com synopses rarely catch the real essence of the story.
The Free Jaffa use the Dakara, ancient super-weapon, via the Stargate to wipe out a world that was just about to receive Origin. One in which SG-1 just happen to be there undercover.
Landry and Bra'tac try to have them reconsider it's use again. It appears that it has been used against human worlds, but not against Jaffa worlds. There is disagreement and their mission fails.
Meanwhile, SG-1 discover that all life on the planet was not destroyed. Adria still survives. Now this is what I don't understand: What exactly is Adria? The weapon kills all organic life (Reckoning Pts 1&2). All humans were destroyed. All Priors were destroyed. I thought Adria, was either a Prior, or a human endowed with extra powers. It now appears she is something entirely different. How is Vala her mother - genetically her mother, or simply her birth mother?
Adria takes the Ori ship, with SG-1 hiding aboard, to attack the Jaffa seat of government and the super-weapon on Dakara. SG-1 attempt to stop her, but in a rare failure for them, cannot prevent the destruction of the Jaffa and their ships. They do however manage to escape themselves at the very last moment.
Painting by numbers!