Piper and Leo go to Phoebe's apartment where the Book of Shadows is. 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. She summons Coop and asks to borrow is ring so she can go back in time. Coop agrees but warns it doesn't always work as desired. Leo goes with her and the two of them go into the past in 1975 where they meet a young Victor and Patty in bed, when Piper was 3 and Phoebe hasn't been born yet. Later they try to explain things without giving away too much, and finally revealed Paige and Phoebe are dead and that they're the Charmed Ones. Patty suggests they use their family magic to get Piper to where she needs to go. The three of them take the ring and go to Grams, but end up in a future where Piper and Leo are old and have been waiting for them.
The old Piper and Leo reveal it's 50 years in the future and that Piper needs 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. They try again and see Grams talking with a young Piper. After young Piper leaves, they introduce themselves and Grams faints. Piper reveals that Patty is dead at that time.
Dumain walks Billie through the process for her to travel back into the past. But when he mentions she has to focus on the Triad she suspects something is up and 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. Grams wakes up and Piper makes introductions and tells her she must help save the Charmed Ones. 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 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 all o them prematurely. The present-Billie and Piper merge with themselves in the past, and then Billie and Christy teleports out.
The Angel Of Destiny who brought Leo arrives to take him back again. Piper explains everything but notes they're back where they started. Then the future Wyatt and Chris appear to reveal someone has screwed up their future. Billie and Christy are walking and Christy doesn't believe they're being used and goes off on her own.
Chris and Wyatt explain that Wyatt lost his powers in the middle of a demon fight and came back to the present. Piper figures out Billie and Christy stole Wyatt's power using the Hollow. Coop arrives and Wyatt recognizes him as "Uncle Coop," and then Chris and Wyatt take Patty to see Victor. Victor is confused and finally patty finds out they're separated.
Christy tells Dumain that Billie has abandoned them but there's a way to revive the Triad without her. 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 teleports in to grab Coop and the ring, while Billie shows up and asks to talk to them.
They hear her out and she explains about the Triad, and future-Chris and Wyatt show up and reveal that Dumain is involved. Phoebe calls for Coop who can't respond, and Chris and Wyatt reveal that Coop was sent so Phoebe could fall in love with him, and it wasn't 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.
Dumain is talking with the Triad in the past when Dumain and Christy arrive, but the Charmed Ones and Billie arrive as well and destroy the Triad, then both Dumains. The Halliwells explain that Billie sent them back, and Paige takes the ring. Christy accuses Billie of betraying her but she throws a huge fireball. Billie deflects it back and destroys her.
All the Halliwells are reunited at the Manor and Wyatt has his powers back. They reveal Billie has gone her own way. The Angel of Destiny arrives with Leo and reveals that's how the battle was supposed to end, and it's all worked out. Victor and Patty arrive with the children and Coop reveals he can take everyone back and make sure they won't remember what they've learned. Everyone has a happy moment before going their ways.
Later Piper comes down and says they should write everything down in the Book of Shadows. Each write down what they've experienced and we see what will happen in the future. Coop and Phoebe marry and have three children, and Phoebe publishes a best-selling book. Henry continues to look after his parolees and has three children with Paige, who continues to help the next generation of witches. And Piper and Leo trained Chris and Wyatt and finally opened a restaurant, while Leo trains at a reclaimed Magic School. It ends with an elderly Piper reading their saga to her granddaughter, then going upstairs with an elderly Leo past the pictures of all their family, past and present, on the walls. The other grandchildren come into the manor and the doors swing closed one final time.