The Halliwells make their way through the Underworld, holding the Book of Shadows. Meanwhile Dumain reports to the Triad that things are underway and all going according to plan.
Christy checks in with Billie, who has sent the remaining magical elements home. Billie still has doubts about her “destiny” and Christy suggests they use vanquishing potions against the sisters. Coop arrives and Christy lies to him about what happened, and that they don’t know where Phoebe is. He mentions Phoebe was under a spell before taking off, and Billie wonders since that confirms Phoebe’s claims.
The sisters vow to continue despite Paige’s concerns and they agree to fight Billie and Christy no matter what. Demons appear to attack them and they flee. Another demon named Nomed shows up at Phoebe’s office and suggests to Elise that Phoebe’s absence is cause for concern. He then then talks with his cohort, Zohar (neither of them is named on-camera) and wonders why the Halliwells are hiding in the Underworld, and suspects the Triad.
Victor Bennett is taking care of Chris and Wyatt when Coop teleports in. Victor threatens him with Wyatt's powers, until Coop gets Wyatt to drop his force field, proving they're on the same side. Coop wonders where Phoebe is and Victor is reluctant to talk to him. Coop admits he’s in love with Phoebe and asks Victor to say his name to summon him when he finds Phoebe.
The Halliwells have sneaked into the manor and are working on a potion. When they’re finished they go through the manor until Billie and Christy find them with their own potions. It turns out that Billie astral-projected herself and Christy to fool the Halliwells, then the real Jenkins’ sisters show up and they throw all their potions simultaneously. Christy is hurt and Piper is seriously injured, and Paige orbs them out to Phoebe’s apartment. But Nomed traps and knocks them out, and asserts he needs them as much as they need the demons.
The Halliwells wake up and Nomed reveals the Triad are back and responsible, and he needs their help to kill the Triad for “personal reasons.” He adds that the Charmed Ones destroyed the old guard (the most powerful demons in existance), and up until they were destroyed the younger generation of demons have been unable to take power. They won't be able to pose a threat until the next generation is ready. Piper considers the matter and for a brief second notices a ghostly image of Leo that no one else can see. Piper agrees and the demons fade out back to Magic School. Billie is there tending to Christy’s wound and Billie is still worried. Dumain shows up to find out how they’re doing and then meets with the Triad. They say they need the Hollow, an uncontrollable power that Good and Evil both banished and drove the Source insane, and that Dumain can get the power to acquire it.
Back at Phoebe’s apartment, the Halliwells are preparing for another battle when their demon allies appear to brief them on the Hollow. Piper determines they need to get the Hollow first. Coop arrives and Phoebe quickly pulls him aside. Unfortunately for Coop, Phoebe is overwhelmed by everything and makes him leave, breaking his heart in the process. Coop leaves and Phoebe goes back to tell them to go ahead with the plan.
Victor is getting the kids ready for a bath in the next room when Dumain appears to get Wyatt and Chris, who protect themselves with Wyatt's shield. Dumain persuades Wyatt to orb back home where Billie is there. Dumain then arrives and tells Billie they must use Wyatt’s power to summon the Hollow.
As the Halliwells try to figure out a way to control the Hollow, the demon warns that the sisters must destroy not just the Jenkins sisters but the Triad as well to eliminate the main threat. Leo appears again to Piper alone and she says they must go ahead with the plan.
Victor is trying to contact the Halliwells while Billie yet again expresses her concerns about using Wyatt, and Billie once more reassures her they have to kill the Halliwells first. Billie finally gives in again and they prepare the spell while the Halliwells cast their spell to summon the Hollow at the same time. The Hollow splits and all five sisters have absorbed the Hollow. Victor tries to convince Chris to take him to Wyatt.
Dumain orders Billie and Christy to take Wyatt’s powers and they do so. But Chris orbs Wyatt back to him and Billie and Christy attack Dumain, who makes a hasty escape. The Halliwells turn on the demons and the Nomed escapes using Zohar as a diversion. Then Zohar throws an energy ball at Pagie when it hits her the glow of his powers go into Piper, Phoebe, and Paige. Then Piper, Phoebe, and Paige throw 2 energy balls (one from each hand) at Zohar vanquishing him in the process.
Dumain goes to the Triad and warns that the Jenkins can’t be controlled, but the Triad are unconcerned. The Halliwells arrive and obliterate the Triad then orb to confront Billie and Christy at the manor. They open fire on each other, but their power is now evenly matched. Their fire blasts and energy beams meet halfway, and the power is building, shooting out in all directions and devastating the manor. The energy goes critical, sending all of them flying. The manor explodes, causing the Hollow to return to its containment.
In the fiery aftermath, Piper digs herself free and finds Phoebe’s corpse. And also Paige is dead but her corpse is not shown. The Angel of Destiny appears and summons forth Leo, who goes to Piper. The Angel of Destiny declares the battle over, although “not as she expected,” and then departs. Piper hears someone crying thinking it's Paige (who is dead) but finds Billie and attempts to blow her up. Leo pulls her off and Billie runs to find Christy (who is also dead) and Piper tries to blow her up as she's running. Leo says there’s nothing left for them and they have to go...