Piper and Leo go to Phoebe’s apartment, where Phoebe took the Book of Shadows for safekeeping during the battle. While she looks for some kind of solution, Billie returns to Magic School and confronts Dumain, revealing Christy is dead. Dumain suggests she project herself back into the past and save Christy.
Piper and Leo arrive at Victor’s and Piper breaks the news. Victor reveals he knows about Coop and Piper realizes he can help them; he used his ring to show Phoebe her past loves. She summons Coop and asks to borrow his ring so she can go back in time. Coop agrees but warns it doesn’t always work as desired, because love is emotional, not practical. Leo goes with her. Piper tries to focus on Phoebe, and the two of them go into the past--but end up in 1975, where they meet a young Victor and Patty in bed. At that time, Prue was 5, Piper was 3 and Phoebe hasn’t been born yet; Piper suspects this is the night Phoebe was conceived. Piper and Leo explain things to Patty without giving away too much, and finally reveal that Paige and Phoebe are dead and that they have grown up to become the Charmed Ones.
Patty suggests they use their family magic to get Piper to where she needs to go. She believes that if they can get Grams to travel with them, they can recreate the Power of Three and send away the Hollow. The three of them take the ring and try to go to Grams--but end up in a future where an elderly couple are playing Scrabble. Suddenly, the man asks Leo how to spell Zankou. The woman thinks it's cheating, but the man says he isn't asking her--he's asking himself. It turns out that the elderly couple is the future Piper and Leo--they'd been expecting their younger selves.
The old Piper and Leo reveal that it's 50 years in the future, and that Piper is "Grams" now. They also tell Piper to focus on who she wants to get to with her heart, not her head, and they must work together to get rid of the Hollow. Piper and Leo are somewhat relieved that they eventually succeeded. They then focus properly, and end up in 1982 where Piper sees Grams, talking to her younger self. After young Piper leaves, they introduce themselves and Grams faints at the sight of Patty, because she had been dead for four years at the time.
Dumain talks Billie through the process for her to travel back into the past. But when he mentions she has to focus on the Triad rather than Christy, she finally realizes she’s been manipulated. Dumain tells her go back and ask Christy so she’ll understand.
While Patty tries to wake Grams, Leo points out that he could be taken away again, because the final battle won't have been fought. Grams wakes up and Piper makes introductions and tells her she must help save the Charmed Ones. Grams is skeptical at first, but when Piper and Patty tell her she is the grandmother of the Charmed Ones, Grams is gratified and readily agrees to help. Billie projects herself back into the past at the Manor, just as the past Billie and Christy arrive. She warns them but past-Billie sends present-Billie flying into the wall with her telekinesis and goes on to fight. The battle starts to play out as before but then Piper, Grams, and Patty arrive to cast a spell which drives the Hollow out of the five girls. Present-Billie and Piper merge with their past selves; time has caught up with itself. Billie and Christy teleport out. The Angel of Destiny arrives to take Leo back, because the final battle has not been fought.
Piper explains everything to Paige and Phoebe, but notes they’re back where they started. Suddenly Wyatt and Chris appear from the future. They reveal that they were fighting demons in their time when, without warning, Wyatt lost his powers.
Billie and Christy are walking down a downtown street. Christy wants to get back to Magic School so they can get Dumain's help to kill the Charmed Ones. Billie tries to tell Christy that Dumain and the Triad have been using them all along. Christy isn't willing to listen, even when Billie tells her that Dumain tried to get her to go to the Triad first. Christy heads off to Magic School on her own. A disillusioned Billie realizes that her sister has become a killer.
Back at the manor, Chris and Wyatt explain that Wyatt lost his powers in the middle of a demon fight and they came back to the present to find out how. Coop arrives and Wyatt recognizes him as “Uncle Coop,” leaving Phoebe shocked. Chris, Wyatt and Patty orb to Victor's apartment. Christy tells Dumain Billie has abandoned them but there’s a way to revive the Triad without her. Meanwhile, Grams is working on a potion when Henry arrives to talk to Paige. Coop insists on confessing his love to Phoebe but Phoebe can’t handle it and goes to talk to her sisters after giving him the ring back. Dumain shimmers in to grab Coop and the ring.
Billie arrives and asks to talk to the sisters. They have vanquishing potions at the ready, but hear her out. She tells them that the Triad and Christy have been using her all along, and admits that she and Christy stole Wyatt's powers while they were infected with the Hollow. Future-Chris and Wyatt show up and reveal that Dumain is involved. Piper realizes they have to go back in time--but to before they summoned the Hollow, so they can get Wyatt's powers back. Phoebe calls for Coop, but he doesn't respond.
Chris and Wyatt reveal that the Elders sent Coop to Phoebe so she could fall in love with him. They wanted to make up for all she'd sacrificed over the years, as well as for all Piper and Leo had to endure, so it won't be a forbidden love. They explain that in the future they’re as one and all she has to do is think about him to summon him. She does so and he appears, in great pain. He reveals Dumain took his ring and they plan to go back in time to warn the Triad. Billie thinks they've already gone back, but she can go back in time as well.
Dumain and Christy find past-Dumain talking with the Triad. They try to warn the Triad that they have to get the Hollow before the Charmed Ones do. Just then, the Charmed Ones and Billie arrive as well. The Charmed Ones vanquish the Triad with potions, then Piper blows up present-Dumain. Past-Dumain starts to shimmer away, but Piper blasts him in mid-shimmer and blows him up as well.
The Halliwells explain that Billie brought them back by projecting herself to Christy. Before Christy can react, Paige orbs the ring from Christy's finger. Christy accuses Billie of betraying her. Billie begs Christy one last time to give up evil. Instead, an enraged Christy launches a huge fireball at them. Billie telekinetically deflects it back, vaporizing Christy; realizing she has just killed her sister and that her entire family is gone, she breaks down in tears as the Charmed Ones comfort her.
All the Halliwells are reunited at the Manor and Wyatt has his powers back; he happily orbs to his mother's side to show them. They reveal Billie has gotten back her own way and needs to be alone for a bit. The Angel of Destiny arrives with Leo and reveals this was how the battle was supposed to end. Victor and Patty arrive with the children and Coop reveals he can take Patty and Grams back and make sure they won’t remember what they’ve learned. Patty reveals that Victor told her Prue is dead, and it's one thing she wants to forget. Everyone shares a happy moment before going their separate ways.
The next day, Piper comes down and suggests that she and her sisters should write everything down in the Book so they can pass it down the way it was passed down to them. Each write down what they’ve experienced and we see what will happen in the future. Coop and Phoebe marry (the Angel of Destiny presides) and have three daughters while Phoebe publishes a New York best-selling book called "Finding Love". It also shows Billie and the sisters remain very close friends. She is seen babysitting Phoebe's two eldest daughters while Phoebe and Coop appear to be running to the hospital to deliver their third daughter.
Henry continues to look after his parolees and has a son and twin daughters with Paige, who continues to guide the next generation of witches and future whitelighters after embracing her whitelighter side. Piper and Leo have a daughter, named Melinda. Piper also follows her own dreams of opening a restaurant, while Leo once again becomes headmaster of the reclaimed Magic School and helps to train the next generation of witches until he retires. By then, Wyatt, Chris and Melinda have already taken over the fight between good and evil. The story suddenly goes forward to the year 2050 where it ends with an elderly Piper reading the last lines of their saga to her granddaughter, Prudence, before going upstairs with an elderly Leo as they pass the pictures of all their family, past and present, on the walls. The couple's other grandchildren run into the manor and Prudence telekinetically swings the doors closed for a final time, using her namesake's distinctive flick of the hand. As they do, we see a final flash of the triquetra, symbolizing the Power of Three.