Jonas: As the conversion process goes deeper, the heat and pressure get higher.
Carter: And naquadria is highly unstable.
Jonas: We believe that when it reaches a certain depth, it's going to explode. With enough force to obliterate Kelowna.
Jonas returns to request the team's help after making a discovery about the conversion of naquadah to naquadria inside his planet's core that could have potentially devastating consequences. Carter joins Jonas and his research assistant/new girlfriend Kianna in a plan to halt the conversion by tunneling deep beneath the surface of the planet in the Kelownan government's state-of-the-art Deep Underground Excavation Vehicle, but the mission is complicated by the reveal that Kianna is actually a Goa'uld spy in the service of Ba'al. On Earth, Daniel and O'Neill attempt to negotiate with representatives from the planet's three superpowers about a potential relocation, but become frustrated by their political infighting.
Last appearance of Jonas Quinn.
"Fallout" provides examples of the following tropes:
- Becoming the Mask: It seems that the Goa'uld possessing Kianna really did develop feelings for Jonas, despite initially using him as a means of getting close to the naquadria research.
- The Bus Came Back/Put on a Bus: Jonas returns after permanently leaving the team at the beginning of the season; however, he soon departs again once the crisis has been averted, and this episode marks his final appearance on the show.
- Continuity Nod:
- It's mentioned that no other Goa'uld knew about the existence of naquadria before Anubis probed Jonas's mind, indicating that it is not a naturally-occurring element.
- Hammond offers the Langarans the option of relocating to Madrona.
- Carter realizes that the conversion of naquadah to naquadria was triggered by the Kelownans testing their naquadria bomb.
- Convection, Schmonvection: The excavator passes directly through a magma flow and none of its occupants seem to suffer any ill effects beyond getting a little hot, despite the hull reaching temperatures of 1200 degrees.
- Enemy Mine: Despite the fact that none of them really trust her, Carter, Jonas and Teal'c are forced to accept the help of the Goa'uld possessing Kiann since she designed much of the excavator and is the only one who understands it well enough to make it work.
- I Gave My Word: Jonas claims that this is the only reason he insists on waiting for Kianna after she risks her life to halt the conversion of the naquadah, though it's implied he's not being entirely truthful.
- Homeworld Evacuation: Daniel and Hammond offer this as an alternative to the Langaran delegates in the event that Carter and Jonas are unsuccessful in their mission.
- Made of Explodium: Jonas is concerned that if the conversion process of naquadah into naquadria goes any deeper into the planet's core, it will become so unstable that it could trigger a chain of events that would lead to the destruction of the entire planet.
- Meaningful Rename: Jonas's homeworld — whose previous name was never stated — has apparently been renamed "Langara" to signify the new union between its three superpowers.
- The Mole: It's revealed that Kianna is a Goa'uld in the service of Ba'al, sent to Kelowna to investigate why Anubis was so interested in the planet. Given the exigencies of the plot she became the Mole in the Mole.
- My Species Doth Protest Too Much: The Goa'uld inside Kianna is pretty much the only one in the entire series shown to be capable of caring for humans and acting somewhat selflessly, though she still has her own agenda.
- Nice Job Breaking It, Hero: For a given definition of "hero", as it's revealed that the Kelownan government deploying their naquadria bomb is what triggered the conversion reaction now endangering the entire planet.
- No One Gets Left Behind: Jonas refuses to leave Kianna behind when she successfully delivers the bomb, despite the fact that the excavator is rapidly losing power.
- Nuke 'em: The plan that Carter and Jonas come up with to halt the conversion process involves detonating a nuke inside a fault deep beneath the surface of the planet near to the naquadria vein.
- Omnidisciplinary Scientist: Jonas was explicitly a social scientist when he was first introduced and fulfilled a role similar to Daniel's as the team diplomat/anthropologist during his tenure on SG-1, but seems to have since moved on to the kind of physics and engineering that's more Carter's domain.
- Rank Up: The former ambassador Dreylock has been promoted to First Minister of Kelowna since her last appearance.
- Red Oni, Blue Oni: O'Neill and Daniel respectively, during the negotiations with the representatives from Langara.Daniel: This is diplomacy, Jack. This is the way the game is played, it takes patience.O'Neill: Yeah? Well, I'm fresh out.
- Spotting the Thread: Carter is able to realize that Kianna is a Goa'uld when she studies the excavator's engines and realizes that they're of a modified Goa'uld design.
- The Starscream: Kianna admits that she hasn't told Ba'al about the naquadria because she's planning on stabbing him in the back and taking it for herself.
- Villain's Dying Grace: When the excavator drill breaks down just short of reaching its goal, Kianna offers to climb down the last kilometer alone using Tok'ra crystals in order to plant the bomb, exposing herself to extremes of temperature and noxious gases in the process. After making it back to the surface, the symbiote deliberately saves the life of the host before dying, something that's practically unheard of for a Goa'uld.
- We ARE Struggling Together: The representatives from the various nations of Langara seem to disagree on just about everything and aren't shy about voicing their mistrust of each other, despite the fact that they're facing the potential annihilation of their entire planet.
- Whole-Plot Reference: The plot of the episode could largely be summarized as The Core IN SPACE!
