Samantha Carter is running experiments in her lab back on Earth, trying to deduce the properties of a strange metallic substance that SG-18 brought back from a Jaffa world the previous day. She tries running a small electrical current through it, but the capacitor spikes, and she is thrown to the ground in a heap of sparks and fire.
She is rushed to the infirmary, but her ankle is sprained, so she won't be able to join her team on a mission to P7X-914 later that day. Luckily for SG-1, Dr. Rodney McKay is just arriving in the gate room, coming back for a short leave from Atlantis. But instead of getting some R&R, Mitchell and Daniel talk him into joining them offworld for the mission, replacing Carter for this one time only.
A quick trip step through the stargate and the team (sans Teal'c, who is still doing work on Chulak) arrives on 914 amid, surprisingly, a firefight. A small group of Jaffa are being engaged by a larger force of humans, who have them pinned down behind a rock outcropping. At once, Mitchell, Daniel, and Vala rush forward to assist the Jaffa, but McKay lags behind, not quite knowing which side is the allied one. One of the humans sees him and runs towards him, pulling out a pistol. But before he can fire, a Jaffa warrior zats him; after this, McKay joins the others.
With SG-1's help, the humans are quickly pushed back, and they retreat into the nearby woods. Mitchell asks the lead warrior what's going on, and he replies that those men were from the Lucian Alliance. Apparently, their new leader is trying to muscle his way into control of outlying worlds, and he's doing a much better job than Netan ever could. A planet in a nearby system has dropped out of contact, and they think it's only a matter of time before this world falls, as well.
In the meantime, though, the Jaffa bring the team back to a nearby city, one of five that were set up around the stargate back in the days of the System Lords. They're offered lodgings for the night, as the Lucian Alliance troops will do doubt be guarding the gate now.
While Mitchell and Vala head out into the city center to gather information, McKay and Daniel discuss life on Atlantis; Rodney feels a little left out there, never knowing quite where he belongs. Daniel sympathizes with him, remembering the days when he always felt out of place on SG-1. But he convinces McKay that the feeling will pass with time, and eventually he'll see John Sheppard the way he himself sees Jack O'Neill.
Suddenly, the sound of gunfire and staff blasts sound from the square, and the two look out the window to see Col. Mitchell and vala pinned down by... Jaffa!? Cam takes a direct staff hit to the chest and goes down hard, and Vala is zatted a few seconds later. Then, the attackers glance up at the building where Daniel and McKay are waiting, and they rush to the entrance.
Knowing they don't have much time, Jackson grabs their gear and weapons and throws them out onto the ledge outside the window. He seings outside and motions for McKay to join him, but he refuses to budge, afraid he'll fall. With the sounds of feet coming closer, Daniel reaches in and yansk Rodney outside with him, then the two clamber onto the rooftop next to theirs, barely evading the traitorous Jaffa in the process.
Down in the city square, Mitchell and Vala are being taken away, along with the Jaffa that met them at the gate. Obviously, some of the people here were spies for the Lucian Alliance, and decided to round up those they could. From their place on the room, McKay and Daniel watch, helpless. After collecting their things, they sneak into another building via window, steal a pair of cloaks, and head downstairs into the marketplace.
Two dozen Jaffa and humans are walking about, keeping the citizenry in check. There are rumors that the other cities are being ambushed, as well, and that reinforcements are coming through the stargate to control the populace. Someone waves to the two Earth doctors, motioning for them to come into a nearby pub. They do so, and sit down with a trio of men who claim to have a stash of weapons.
The men want to get rid of the Lucian Alliance, but know that there's no way to do it without help from the Jaffa Nation at large. So they have an idea; take zats and stun their way to the gate. Then, they and some others will hold off the enemy while McKay and Daniel get through to Chulak and call for aid. McKay doesn't want to do it, afriad that they'll get captured with ease. But Daniel assures him that he's escaped worse situations, and the duo agrees.
An hour later, they launch their attack. Eight Jaffa come out of the forest near the gate firing, taking down half of the Lucian guards at once. A tense firefight ensues, in which Daniel slowly advances on the DHD. He starts to dial, but one of the enemy zats him from behind, and he collapses. McKay, knowing he needs to do this, rushes out, clumsily stuns the human, "bad" human, and dials Chulak, punching in the last symbol Daniel missed.
The gate activates, and he drags himself and Dr. Jackson through...
((A few hours later))
The stargate activates again, and dozens of Jaffa pour through, along with a few Goa'uld-esque tank-like vehicles the Jaffa have constructed under Bra'tac. McKay, Daniel, and Teal'c come through, as well, and they move toward the city. As sounds of very little staff blasts break out (the majority of the Lucian Alliance men are surrendering), Daniel congratulates McKay; he saved the day.
Back at the ISGC, McKay is preparing to head back to Atlantis. But just as he's about to leave, Carter comes in the gate room on crutches, thanking him for being so brave. She gives him a light peck on the cheek, then watches as he heads home.