When Xander takes a mystical hit from the demon Toth that was intended for Buffy, he wakes up to find a mysterious double living his life in his place—and, frankly, doing a much better job of it.
Xander and Anya watch a movie with Buffy and Riley while listening to the background noise of Xander's drunken parents fighting and yelling upstairs. The next day, the gang looks at a potential new apartment for Xander. He doesn't think he can afford it and this upsets Anya. Giles receives a visit from a demon searching for the Slayer. He later identifies the demon as Toth, only survivor of the Tothric Clan.
The Scoobies check out the city dump in search of the demon and find Spike collecting. The demon hits Xander with light from a rod and knocks him to the ground. He gets to his feet and walks off with the rest of the gang, but there is another Xander still lying in a pile of trash. The next morning, one Xander awakens at the city dump and then discovers his double upon returning to his house. Meanwhile, Spike has put together a Buffy doll from mannequin parts which he uses to practice beating up on.
One of the Xanders is very ambitious and gets a promotion at work, signs a lease for the apartment, and sets up a date with Anya. The other, insecure Xander watches as all this happens and finally confronts his double. After the two Xanders see each other, the confident Xander talks to Buffy and she makes this a matter of Slayer business.
Soaked by the rain, weak Xander goes to Willow and tries to explain that this double is taking over his life. He tells Willow that the double is doing a better job of living his life but then suddenly realizes that his double is going after Anya and that is one thing he won't allow.
Anya and the Xander double discuss their future and Anya expresses her fears about not living forever. Giles discovers that the rod Toth used split Xander into two real Xanders, one with weak qualities and the other with strong qualities. The weak Xander crashes the date between strong Xander and Anya. Both think that the other is a demon and the weak Xander pulls out a handgun he got from Anya's apartment.
Buffy tells the doubles the truth about their situation and tries to convince them not to kill each other. Toth appears at the apartment then Buffy and Riley fight and kill him. They eventually begin to get along, and their actions become so similar to each other that the comment is made that Xander is a "bad influence" on himself. Giles and Willow research and come up with a way to reunite the two Xanders but Anya expresses disappointment over this as she wants both to stick around for some sexual shenanigans, much to the disturbance of the others. Willow ends the spell (literally—she simply says "let the spell be ended") on the Xanders and makes them one again. While moving Xander into his new apartment, Xander and Riley talk. Riley confesses that despite how much he loves Buffy, he realizes that she doesn't feel the same.
While the viewpoint generally follows the "weak" Xander, the episode (like "The Zeppo") establishes that Xander is neither completely helpless nor useless. While we are led to believe that "strong" Xander is using mind control to obtain the promotion and the new apartment, in fact these things were earned by Xander already.
Riley reveals to Xander that he knows Buffy doesn't love him back, which serves as the first solid indication of trouble in their relationship and a prelude to their break-up in the coming episodes.
When Buffy and Dawn argue, Joyce grabs her head and refers to her "two teenage girls in the house" headache, all the while looking visibly distressed. While it is implied that she is being sarcastic, this exchange is in fact a prelude to the brain tumor she will develop, beginning in the next episode.
"Weak" Xander brushes off Willow's attempts to calm him down by indicating that how she would handle an evil twin. Afterwards, Willow mutters "Well I handled it fine.", a reference to Vamp Willow from the Wishverse in Dopplegangland.
When Willow asks if one of the Xander's is a robot this foreshadows the Buffybot later in the season.
When Riley helps Xander pack up his things from his parent's basement, Xander claims he envies Riley, for his sanity and not for Buffy, reaffirming "Not that I'm still into Buffy. Not that I ever was." This is a reference to Xander's crush on Buffy in the first and much of the second season.
Xander gets a promotion at his construction job which is the beginning of Xander being shown to have more responsibility on construction sites in later episodes. He's shown as presumably a foreman and in "Lessons" he arrives wearing a suit. In "Showtime" he indicates he may be responsible for multiple construction sites too.
Toth, killed by Buffy with a sword
Behind the Scenes
Nicholas Brendon's real-life twin brother Kelly Donovan is his body double for this episode. In almost all of the scenes Nicholas Brendon played both suave and goofy Xander with his brother Kelly Donovan playing the twin with the non-speaking role. Kelly only spoke in the scenes where both Xanders had speaking lines.
Pop Culture References
Xander's quote "Shoot us both, Spock" is from the Star Trek episode "Whom Gods Destroy" in which Kirk tells Spock to shoot both himself and Garth of Izar disguised as Kirk. But this episode is actually an homage to the Star Trek episode "The Enemy Within" in which Kirk is split into his two emotional halves.
Xander makes a comment about his Babylon 5 commemorative plates. While such plates were planned, they never actually went into production.
While talking to the apartment building manager, Xander jokes about buying a Klingon costume, which references Star Trek.
The dubbed kung-fu movie that the gang is watching is Duel of the Iron Fist.
In a DVD feature highlighting the demons of the season, Jane Espenson reveals that Toth was named so just so she could work in the joke about "toth" being British slang.
This episode is Xander-centric.
Xander - "Maybe it's time to start looking for a new place ... Buffy you've been to Hell. They had one bedrooms, right?"
Xander - (after Buffy and Riley make out in the new apartment's bedroom) Guys, you can't save it for the bedroom? (they look around the bedroom) Okay, good point.
Buffy - "Well, if this guy wants to fight with weapons, I've got it covered from "A" to "Z" - from ax to ... zee other ax."
Xander - "So you bought the magic shop and you were attacked before it opened. Who's up for a swingin' chorus of the "We told you so" Symphony?"
Riley - "Psychologically this is fascinating, doesn't it make everyone wanna lock them in separate rooms and do experiments on them? Just me then."
Giles - "We just, uh, need to arrange the candles. Also, we should continue to pretend we heard none of the disturbing sex talk."
Willow - "Check. Candles and pretense."
Xander - "Hey, wait till you have an evil twin. See how you handle it."
Willow - "I handled it fine."
Xander - "I just thought you could help carry a little."
Anya - "Me? Buffy has super-strength. Why don't we just load her up like one of those little horses."
Riley - "Hey, I'm well aware of how lucky I am. Like, lottery lucky. Buffy's like nobody else in the world. When I'm with her, it's like... it's like I'm split in two. Half of me is just on fire, going crazy if I'm not touching her. The other half is so still and peaceful, just perfectly content... just knows: this is the one. But she doesn't love me"