With the Ori Army making such advances into the Milky Way, Ba'al intended to capture Adria and take her as a host, by ambushing SG-1's own plan to capture the Orici.
Adria is able to sense deception within others, Vala Mal Doran has hatched a plan: SG-1 implants false memories into Vala with the Galaran memory device, detailing her escaping from Stargate Command, as they had turned against her. Because Vala believes that these memories are entirely real, Adria does not realize that it is part of a deception.
Adria and Vala traveled to the planet in question, only to find SG-1 already there and waiting, and it was revealed that Vala had allowed herself to be implanted with a false memory by the Galaran memory device. However, before SG-1 could take in Adria, Ba'al's Jaffa beam in and kidnap Adria, taking her as a host, and claiming that he would order the Ori Army to leave the Milky Way galaxy.
After implanting himself in Adria, SG-1 boarded his Ha'tak and killed another clone. Ba'al offered to help SG-1 in driving the Ori Army out of the galaxy, saying that the Ori were indeed dead. However, SG-1 contacted the Tok'ra, who removed Ba'al from Adria, presumably killing him, but not before he released his symbiote toxin into her.
But they soon realized it was not Adria but Ba'al. They devised a plan to swap Ba'al out for a Tok'ra but this plan failed when Ba'al released his symbiote toxin into her system in attempt to kill her so that the Tok'ra could not retrieve the knowledge she possessed. Ba'al was extracted but not soon enough for Adria to take over the Odyssey before she Ascended.