As the birth of baby Chris approaches, the sisters prepare to send adult Chris back to the future. They write a spell, which Gideon tweaks:
In this place and in this hour, we call upon the ancient power,
Open the door through time and space, create a path to another place.
Instead of sending Chris to the future, however, it sends Chris and Leo to an evil parallel universe. At the same time, Evil Chris and Leo appear in the good world. Evil Chris shoots a Darklighter's arrow at Paige, but she deflects it. Evil Chris and Leo black-orb out, then head to the top of the Golden Gate Bridge to consider their next move.
"We've got to get back to our world," Evil Leo says. "We're going to need the Power of Three to do that."
"Well, we can't trust those Pollyanna witches," Chris complains. "They're too good. God, who do I have to kill so we can get out of here?"
"I think I might know somebody," says Evil Leo, "somebody we can use to force the sisters to help us."
They find Darryl and beat him up. Paige and Phoebe, after scrying for evil activity, orb in and trap Evil Chris and Leo in a crystal cage. Paige offers to orb Darryl to Gideon for healing, but he refuses. He no longer wants anything to do with the Charmed Ones. Inspector Sheridan suspects that Darryl may have helped Chris break out of jail, so Darryl can't risk any further contact with the Halliwell family.
The sisters consult with Gideon about how to return Evil Chris and Leo to their own world. They decide that the best course of action is for Phoebe and Paige to go to the evil world to get good Chris and Leo. They assume that Evil Phoebe and Paige will in turn go to the good world to get Evil Chris and Leo. But the exchange between the worlds has upset the balance, and they're no longer operating exactly in parallel. Paige and Phoebe cross over, but their counterparts don't. So they go to find Chris and Leo on their own.
Since the worlds are opposite, Phoebe reasons that the good beings in the evil world would be equivalent to the evil beings in the good world. So they go to the lair of the most powerful evil being they know of in their own world--Barbas.
Phoebe and Paige arrive in the Underworld to find it a beautiful garden with gurgling fountains. Dressed in white is Barbas, Demon of Hope, talking to good Chris and Leo:
"Your presence here gives me great hope, the hope that someplace there really is a different kind of world, a world where the greater good…the goodness of the heart prevails."
Leo and Chris are relieved to see Phoebe and Paige. But their relief is short-lived; the next moment, Evil Phoebe and Paige arrive. They attack their good counterparts, but both sides think alike and are too evenly matched for either one to prevail. They stop fighting when Piper calls, saying she's in labor. Meanwhile, Good Barbas reveals to Leo and Chris that Gideon might have intentionally caused the imbalance between the worlds: Gideon was desperately hoping to eliminate Wyatt.
With Piper in labor, Gideon makes his move on Wyatt. Using an athame, he breaks through Wyatt's shield. But Wyatt uses telekinesis to stab Gideon with his own athame. The two Phoebes and two Paiges recite a spell to eliminate the threat to Wyatt:
We call upon the ancient lore to punish with the power of four,
Strike down this threat from both there and here, make him suffer, then disappear.
Both Gideons orb out in the nick of time. In their respective rooms at Magic School, they heal each other through a mirror between the worlds. Meanwhile, Paige, Phoebe, Chris, and Leo travel back through the portal to their own world, and Evil Chris and Leo do the same.
Believing that that balance has been restored, Phoebe and Paige prepare to visit Piper at the hospital. When they step outside, though, something is off. A rainbow appears in a clear sunny sky, children are playing, neighbors smile and wave happily. Mrs. Noble, who lives next door, reminds Phoebe that she parked her car blocking Mrs. Noble's driveway.
Phoebe apologizes. "I was just coming out to move the car…I won't park there again, I promise."
A patrol officer approaches. "That's right. I know you won't." He pulls out a gun and shoots Phoebe at point-blank range. She falls backward into Paige's arms.
"Wrongs must be righted," the patrol officer says.
With Paige calling for help and Phoebe bleeding to death, Mrs. Noble says, "Have a super day!"