"We don't leave our people behind."
— Col. Jack O'Neill
Carter, Daniel, and Teal'c return from a mission claiming that O'Neill and a new addition to the team named Lieutenant Tyler are stranded on the planet under heavy enemy fire, but no one else at the SGC has any recollection of a Lt. Tyler existing. As O'Neill and the mysterious Tyler wait to be rescued, Colonel Simmons arrives to conduct an external investigation into the rest of the team.
"The Fifth Man" provides examples of the following tropes:
- Anti-Air: O'Neill uses a grenade launcher to shoot down a Death Glider.
- BFG: At the end of the episode, Teal'c takes the cannon version of the staff weapon from the downed Death Glider and uses it as his own personal weapon.
- Backstory Invader: Tyler eventually comes clean that he's an alien who secretes a pheromone that makes one perceive them as a familiar (even if fictitious) figure they have always known. Since he was running from their mutual enemies they let him go. In later episodes, they use the memory-altering compound to infiltrate enemy organizations.
- Big Damn Heroes: Carter, Daniel, and Teal'c return to the planet just in time to save O'Neill and Tyler when they're cornered and out of ammo.
- Conflicting Loyalty: Simmons accuses Daniel of this as a result of Sarah's status as a host, claiming that his judgement is clouded by his emotions.Daniel: I lost someone I care about. And not for the first time, I might add. You think that makes me sympathetic towards the Goa'uld?
Simmons: I think that makes you someone whose judgement can be easily clouded. And for a man in your position that's… unacceptable. - Continuity Nod: Daniel suggests that he, Carter and Teal'c might have somehow traveled to an alternate reality where Tyler doesn't exist, as the situation bears some resemblance to the time he went through the quantum mirror and nobody on the alternate Earth knew who he was.
- Fake Memories: The team all have fake memories of Tyler being on the team going back several weeks. Fraiser also has a brief recollection of him after she accidentally comes into contact with the residue left on Teal'c's jacket.
- Heel–Face Revolving Door: Simmons uses Teal'c's recent brainwashing by Apophis in order to accuse him of this.Simmons: Teal'c changes sides more often than I change the oil in my car.
- Heroic Sacrifice: Defied; Tyler tries to pull one of these by leading the Jaffa away so that the team can go through the gate unhindered, but they refuse to leave him behind and go back to rescue him instead.
- If I Wanted You Dead...: When Simmons asks why he should trust Teal'c after he had been brainwashed Teal'c's response is that if he were still loyal to the Goa'uld then Simmons would already by dead. He follows this with a look that makes it clear that Teal'c's loyalty to Stargate Command is the only reason he doesn't kill Simmons for questioning his loyalty.Teal'c: If I were still loyal to the Goa'uld, you would know it.
Simmons: Really?
Teal'c: It would be immediately apparent, as I would not hesitate to kill you where you sit. - Lie to the Beholder: Tyler's race, the Reol, naturally produce a substance that can make them appear as members of another race as part of an inbuilt defense mechanism.
- Line-of-Sight Alias: Lt. Tyler apparently got his name from the M.R.E. package that showed it came from Tyler, Texas. He later states to O'Neill that he was from Texas, but his family moved around a lot.
- Major Injury Underreaction: Tyler reacts to the gaping wound in his leg by saying that it's "not a problem", though this is somewhat justified by the end as it's revealed that he has advanced healing capabilities.
- No One Gets Left Behind: A major theme of the episode; Carter, Daniel, and Teal'c are adamant about returning to the planet to rescue O'Neill and Tyler, while O'Neill refuses to leave Tyler to save himself, going back for him even after the reveal that he's not a member of the team.
- Obstructive Bureaucrat: Simmons is revealed to have been keeping tabs on the SGC and uses this latest incident as an excuse to carry out a formal investigation of Daniel, Carter, and Teal'c.
- Passive-Aggressive Kombat: Daniel is somewhat grouchy after being zatted.O'Neill: Hey, where's Tyler?
Daniel: You know I would have asked him but I was too busy being unconscious after he shot me with that zat you gave him, so… - Running Gag: O'Neill offers to take Tyler fishing.
- Weirdness Magnet: Lampshaded while Simmons is interviewing Carter.Simmons: You were briefly taken over as a host by the Goa'uld, once you fell under the control of an artificial intelligence of alien origin, and the last time we met you harbored an alien in your own home.
- What You Are in the Dark: All over the place.
- "Tyler" reveals himself to O'Neill when it becomes clear that he'll die to defend who he believes to be his team member. O'Neill has no reason to doubt his identity, but Tyler is unwilling to let him sacrifice himself under false pretences. He comes clean and urges O'Neill to leave him. O'Neill refuses.
Tyler: I cannot let you do this, Colonel.
O'Neill: Do what?
Tyler: I cannot let you die protecting me.- After Tyler's Heroic Sacrifice, the team have the opportunity to escape, but go back to rescue him instead. This is partly pragmatic - as O'Neill points out, they can't afford for the Goa'uld to replicate his species' ability to infiltrate - but also because, well, they're unwilling to let him be experimented on.
