The team find themselves in an underground complex where they are forced to perform industrial labor, with no memories of their old lives and seemingly brand-new indentities: O'Neill is now "Jonah", Carter is "Thera", Daniel is "Carlin" and Teal'c is "Tor". They soon begin to suspect that something is amiss, and have to work together in order to uncover the truth about their situation.
"Beneath the Surface" provides examples of the following tropes:
- Ask a Stupid Question...:Carlin: What did you do in the mines?
Jonah: I mined.
- Bait-and-Switch: There's a throwaway joke of this form when Jack and Sam are trying to remember their old memories. Jack says he remembers a bald man who wears a short-sleeved shirt who's "very important to me", seemingly referring to General Hammond, but then:Jack: I think his name is... Homer?
- Catapult Nightmare: Lampshaded on the DVD Commentary:Peter DeLuise: You always know when you're dreaming when someone wakes up like this. You always find that when you are dreaming and you wake up, you always go up into frame as well instead of just opening your eyes. It's obligatory.
- Chekhov's Gun: Near the beginning of the episode, Kaegan mentions that a worker suffering from "night sickness" once tried to smash the skylights in the ceiling of the plant. O'Neill later shoots out one of the same windows to prove to the workers that the surface of the planet is not uninhabitable as they've been told.
- Disproportionate Retribution: Administrator Calder has the team's memories erased, forces them into slave labor and later threatens to send them into the frozen wasteland outside the dome, all because they "passed judgement" on him.
- Domed Hometown: The city is kept under a dome to protect it from the planet's ice age; unbeknownst to the workers, who are kept in the dark in order to provide energy for the city.
- Fake Memories: The team — and presumably the rest of the workers — have their old memories erased and are given a "memory stamp" that provides each of them with a new identity, ostensibly to stop them from asking too many questions. It doesn't really work, however, as they soon find out that they only have incredibly vague memories of their lives before they worked in the plant.
- Forgot the Call: Due to the aforementioned memory wipe, the team initially embrace their new lives as slaves, only questioning it as they begin to recall details of their former identities.
- Happiness in Slavery: Calder justifies his treatment of the workers this way, as the memory stamp ensures they don't know any better."It is my honor to serve."
- HeelFace Turn: Brenna, the plant supervisor, pulls one of these, confirming the team's suspicions that their memories have been altered and revealing their true identities once she decides that Calder has taken things too far.
- The Masquerade: The workers are left to believe that the entire surface of the planet is frozen and they're all that's left of the civilization, when in actual fact they're being used as slave labor to provide energy for the inhabitants of the city.
- Perma-Stubble: Jonah and Carlin both sport this look.
- The Power of Friendship: Despite having no memory of their previous relationships to one another, Jonah, Carlin and Thera work together seamlessly to prevent a catastrophe on the plant when one of the pressure valves begins to overload. They then use this connection to help one another remember details of their past lives.
- Running Gag: "It's an expression," said every time one of the characters lets slip something of their former lives and has no idea why, such as Thera calling Jonah "sir".
- Ship Tease: Jonah admits at one point that he remembers "feeling feelings" for Thera, to which she responds by resting her head on his shoulder. Once they've regained their memories at the end of the episode, both O'Neill and Carter appear to feel some regret when they revert back to maintaining a professional distance in their relationship.
- Shirtless Scene: Tor spends much of the episode wandering around without a shirt on; partly justified due to having his abdomen swathed in bandages to hide his symbiote pouch and prevent him from remembering that he isn't human.
- Single-Biome Planet: The surface of the planet outside the domed city is in the midst of an ice age.
- Stock Footage: The shot of the active Stargate in Daniel's dream is reused from "Small Victories". It cuts away just before the point when, in the original shot, Thor stepped out of the gate.
- True Companions: Demonstrated when Fraiser volunteers for the rescue mission to retrieve SG-1, as well as Hammond's single-minded determination to get to the bottom of what happened to them.
- What Could Have Been: According to Joe Mallozzi, the Ship Tease in this episode wasn't a tease in the original drafts. Sam and Jack's alternate personas were explicitly in a relationship. A key component of the episode would be about them having to go back to their old lives, but having to give up their relationship. A legacy component of this subplot is present in the final scene of the episode where at the very end Jack and Sam remember their old lives and after Carter calls him "sir," O'Neill repeats the word sadly.