Chris is looking for materials on time travel at Magic School; he fears about what may happen if he's around when his younger self is born, an event expected to happen soon. He doesn't want to take chances, but he may have to on the time-traveling because of the uncertainty of effectiveness. Paige orbs Piper's luggage back home as they prepare a potion and Gideon prepares a spell.
Gideon enters a secret room and talks to his evil opposite in a magic mirror. The two Gideons are planning to get the Charmed Ones, Leo and Chris out of the way so they can have a clear shot at Wyatt.
Phoebe argues with a neighbor, Mrs. Noble. Her car is blocking Mrs. Noble's driveway because Mrs. Noble is blocking much of the street with a large dumpster. The neighborhood patrolman arrives and gives Phoebe a citation.
Sheila has had a fight with Darryl and comes to Phoebe for support. She had seen an arrest warrant for Chris; she asked him about it and he became angry. Phoebe and Paige try to talk Darryl into tossing the warrant, but he still wants nothing to do with the sisters. Inspector Sheridan walks over and asks about Chris, and Paige feigns ignorance.
Leo and Chris throw a potion at a triquetra on a wall, attempting to return Chris to the future; but nothing happens, and the potion spills on the floor. A few drops of blood fall near the spilled potion. Gideon returns to the mirror; it turns out that he turned invisible and stopped the potion. His evil counterpart did the same thing; both are bleeding. They heal each other. Leo fetches Piper, and Phoebe and Paige and orbs to Magic School. The sisters cast the spell and the triquetra on the wall opens into a portal. Leo and Chris step through the portal and find themselves in a mirror-image world, in which the Charmed Ones are dressed in black clothes. In the original world, an evil Leo and Chris step out of the portal. Evil Chris conjures a Darklighter crossbow (this Chris is half-Darklighter, since the real Chris is half-Whitelighter). He shoots, but Piper freezes the bolt. Evil Leo and Chris black-orb away.
Gideon explains that the spell must not have been specific enough. Instead, it opened a portal to an evil parallel world that exists in tandem with the normal world in order to maintain the cosmic balance. He sends the sisters after the Darklighters.
Evil Leo and Chris stand atop the Golden Gate Bridge. They marvel at how good this world is. Evil Chris drops an empty beer bottle onto the road, causing an accident. He mentions that in his future, he had to save Wyatt from turning good. The two Darklighters try to figure out how to get back to their world.
Phoebe scries for evil Leo and Chris, but can't find them; as they aren't doing anything evil yet. Paige is grabbing crystals; they plan to trap the Darklighters in a crystal cage. Phoebe marvels at how their evil counterparts are trying to track down good Leo and Chris. They find evil Leo and Chris roughing up Darryl; they hope to use him to bring the Charmed Ones to them. While Phoebe distracts evil Leo and Chris, Paige traps them in the crystal cage. Darryl, still on the outs with the sisters, flees. The sisters bring evil Leo and Chris to Magic School.
The two Gideons are playing chess. Evil Gideon has sent evil Phoebe and Paige to the manor so they won't come through the mirror. This will throw the world out of balance, but they consider it a bigger risk to let Wyatt live.
Gideon suggests that the sisters go to the mirror world and find their Leo and Chris. Paige and Phoebe go, but their evil counterparts don't come back through. Evil Gideon warns the good sisters that the cosmic balance is at risk, and that they act quickly.
Paige and Phoebe find their neighborhood in this world is a slum, and are somewhat skeptical of going to this world's manor. The neighborhood patrolman tries to make Mrs. Noble pay him a bribe. She refuses, and he knocks her down. Paige and Phoebe come to her aid, but both the patrolman and Mrs. Noble run away in fright; apparently their evil counterparts are the terrors of Prescott Street and San Francisco.
The good sisters find evil Darryl at P3, which is a strip bar in this world. Phoebe knocks him over and threatens him with a broken bottle, demanding to know where Leo and Chris are. Darryl had arrested Chris and then Leo orbed him out of jail. He tries to hustle them out; he doesn't want Inspector Sheridan, who moonlights as a pole dancer, to see them. Phoebe realizes that they would go to whoever's good in this world, the demons.
Good Leo and Chris find Barbas in the underworld, which looks like a garden in this world. Barbas is the demon of hope, and is dressed in white. Paige and Phoebe orb in and are met by their evil twins. Piper's water has broken, and she goes to the hospital, leaving Gideon alone with Wyatt.
The two sets of sisters plan to knock out their counterparts and get Leo and Chris out. Both Good and Evil Paige orb out at the same time and leap at each other, but collide and fall to the ground. Evil Paige conjures her crossbow and shoots at good Paige, who orbs the bolts away. The two Phoebes trade blows and neither gets the upper hand (even though evil Phoebe has brass knuckles); they're not only evenly matched, but are thinking exactly the same. The two Paiges orb rocks at each other, causing explosions when their orbs collide. Barbas tells Leo and Chris that Gideon is after Wyatt as they take cover. The fight only ends when both Pipers call and both Paiges answer, saying the same thing at the same time.
In the good world, Gideon breaches Wyatt's protective bubble. Wyatt, however, orbs Gideon's athame into his chest. Gideon pulls the athame out and is ready to try again when the two sets of sisters, in the evil world, speak a spell. The spell almost vanquishes both Gideons (evil Gideon is trying to kill evil Wyatt at the same time), but both orb to the mirror in time and heal each other.
With four sisters available, the two sets of sisters open a portal and good Leo and Chris come back to the good world. Chris goes to fetch the evil Leo and Chris and send them back. Since evil Piper is in labor, the good sisters realize their Piper must be as well, and leave the manor to go to the hospital and find a world with a bright sky, a huge rainbow, and everyone talking very chipper, including normally-crabby Mrs. Noble. Phoebe goes down to move her car from Mrs. Noble's driveway but the patrolman shoots her as punishment for parking there.