Beachhead

S9 E6: When Nerus a minor Goa'uld requests an alliance with Earth Gen. Landry and SG-1 don't need Vala to warn them that Nerus can't be trusted. Vala warns them anyway but Landry decides to risk inviting Nerus to Stargate Command. Nerus explains that a mysterious force field has appeared on the planet Kallana. The field surrounds Kallana's stargate and periodically increases in size. Worse the stargate hasn't shut down for two days which violates all known laws of physics. Worst of all there's a Prior of the Ori on the scene. The team is forced to agree with Nerus's frightening conclusion: The Ori must be establishing a beachhead from which to launch their invasion of our galaxy. Landry orders Mitchell and his team to use any means necessary to stop the Ori. To that end he sends along the military's latest superweapon the Mark IX Gatebuster naquadria-enhanced nuclear warhead. He also sends the Mark IX's designer: Lt. Col. Samantha Carter. SG-1's pleasure at working together again is tarnished only slightly by Vala tagging along. Her life is still linked to Daniel's but now in the presence of the full SG-1 team even she can tell that she's just a fifth wheel. SG-1 travels aboard the Prometheus to Kallana where the force field has grown so large that it's visible from orbit. Mitchell Daniel Teal'c and Vala manage to transport down to the planet's surface with the Mark IX. They try to negotiate with the Prior but even the threat of imminent nuclear vaporization doesn't budge him. Suddenly a bombardment of energy weapons rains down from above. Gerak the leader of the free Jaffa has learned of the Ori incursion and demands to take matters into his own hands. At the same time the force field expands again. Out of options Mitchell arms the bomb and transports his team back to Prometheus.Humans and Jaffa alike brace for impact as the Mark IX detonates below. As the shockwave dissipates they are stunned to discover that the force field has only gotten bigger. Soon it will engulf the entire planet and they have no idea what will happen next. Even after Carter uncovers the true enormity of the Ori scheme SG-1 is at a loss to stop it. Unexpectedly only Vala guesses what must be done. And even more unexpectedly she finds the courage to do it...