"Well, I guess we're goin' in."
— Col. Jack O'Neill
SG-1 plus Jacob and Major Davis are sent to retrieve a Goa'uld mothership that has been left floating above Earth's atmosphere with no visible life signs inside. Once they're on board, however, they realize that it might not be quite as deserted as they'd hoped — and to make matters worse, the ship quickly loses power and crashes into the Pacific Ocean, where it begins to fill with water.
"Descent" provides examples of the following tropes:
- Are We There Yet?: Said by O'Neill at the beginning of the episode.
- Brain Uploading: What Carter initially takes to be a virus left behind by Thor turns out to be Thor's consciousness itself, still fused with the ship after the events of "Revelations".
- Brutal Honesty: When Jonas is complaining about being left on the cargo ship:Teal'c: This is your first mission. It may take some time for Colonel O'Neill to gain confidence in your abilities.Jonas: So it was the same for you?Teal'c: No, it was not.
- Call-Back: Jacob warns O'Neill that he can't just "slap a US Air Force sticker on the side of the ship".
- Chekhov's Skill: Jonas mentions near the beginning of the episode that he has memorized the schematics of the mothership, which comes in handy when he is able to remember the location of a control panel that will allow the team access to the glider bays.
- Continuity Nod: Jonas claims that there are rumors O'Neill only gave him the position on SG-1 to avoid having a Russian on the team.
- O'Neill wishes that they can actually keep the Ha'tak ships they manage to get for more than a couple of hours. They made their last one crash into Delmak to kill Aphosis and Replicators.
- The Cynic: Jacob is extremely skeptical about the idea that Thor deliberately sent the ship to Earth as a gift.
- Drowning Pit: O'Neill and Carter get trapped in one of these when the ship automatically seals them in a section of corridor rapidly filling with water. Fortunately, Thor is able to override the command and let them out before they run out of air.
- Friendship Moment: Teal'c has a brief one with Jonas, reassuring him that he will have plenty of opportunities to prove himself in the field.
- Ghost Ship: The mothership, hovering ominously above Earth with no detectable life signs on board.
- Grammar Nazi:Jacob: By who?O'Neill: It's whom.
- Heroic BSoD: Jacob briefly lapses into this when he thinks that Carter and O'Neill have drowned.
- In the Back: Jacob gets shot in the back by one of the Jaffa roaming around the ship, though he gets over it quickly enough.
- Literal-Minded: This exchange after Teal'c informs Hammond that the mothership is empty:Hammond: I don't mind telling you we've all been holding our breath down here.Teal'c: That is most unwise.
- Oh, Crap!: When O'Neill and Carter first notice water seeping in from beneath one of the doors after the ship crashes into the ocean, and then again shortly afterwards when they get sealed in the corridor.
- Red Shirt: Dr. Freisman is quickly killed by one of the rogue Jaffa when he goes wandering off alone.
- Sealed Evil in a Can: A minor example; Jacob accidentally lets three of Anubis's Jaffa loose on the ship after unsealing a corridor, not realizing they were there as they had placed themselves in a deep enough state of kel'no'reem that their life signs could not be picked up by the sensors.
- Self-Destruct Mechanism: When the team first board the ship they realize that the self-destruct has paused partway through its countdown, and Carter later theorizes that Thor is deliberately keeping it frozen. This becomes a problem when they remove Thor's consciousness from the ship's systems as the timer starts up again, leaving the team with just seventeen minutes to get a safe distance away.
- Trojan Horse: Jacob is initially concerned that the ship was deliberately left behind by Anubis as a Trojan Horse with which to attack Earth.
- The World Is Just Awesome: Jonas's reaction to his first trip into space, much to O'Neill's irritation.
