Beachhead

Samantha Carter returns to the SGC when the Ori seize control of a planet named Kallana as a foothold in the Milky Way Galaxy. After several attempts to halt the process, they discover that they have been helping the Ori achieve their goal, instead of foiling their efforts. The Ori have been building an enormous Stargate to allow their ships to enter the Milky Way, but they are stopped by Vala, who apparently dies in the process, although there is a possibility that she got trapped in the Ori galaxy.