The Charmed Ones, Leo and Darryl prepare to attend a Halloween party at P3. Piper is Glinda from The Wizard of Oz, Prue is a fairy, Phoebe is Elvira, Leo wears his Army uniform and Darryl wears his uniform from his rookie cop days. At the same time, Darryl begins to question Leo about his past and who he is from what he is wearing as a costume (his army uniform). Phoebe is offended by the stereotype of witches as hook-nosed crones on broomsticks; and has therefore dressed as Elvira to protest. She has also invited Cole, but he has not arrived.
Two Grimlocks show up on Prescott Street. Although they were vanquished two years earlier, they are among the few demons who know how to return from the dead on Halloween, "when the veil between worlds thin". A boy sees them and comments them on their "costumes." One of the Grimlocks replies by starting to steal his sight. Cole shimmers in and one of the Grimlocks addresses him by his demon name, Belthazor. He tells them not to use that name, and orders them to let the boy go. Cole has a different plan for the witches—one approved by the Triad. One Grimlock comments on how they have always hated Belthazor, while the other one comments on his disguise as a human being.
Prue wants to take a picture of everyone when the doorbell rings at the manor. Phoebe opens the door to the Grimlocks. Phoebe realizes almost too late that they are not in costume. The Grimlocks start to strangle Phoebe and Piper. Leo gets a jingle at the same time, telling him of a time portal that is about to open. He and Darryl rush in to see the Grimlocks strangling Piper and Phoebe. Prue rushes in and flings them aside. A time portal opens up behind the sisters. Piper freezes the Grimlocks, but Leo tells them that they're not what "they" jingled him about. At that moment, the sisters are sucked into the portal, leaving only their wigs.
The sisters land in an open field with a round stone altar in the center. Upon the altar are fruits, vegetables and grain stalks. Riders come out of the woods, crying "Kill the witches!", and the sisters run for cover. The sisters realize they've gone back in time. Prue gets a look at what the witch hunters are wearing, and figures they're somewhere in the 17th century. One of the witch hunters, Micah, discovers them, but tells the others he has found nothing. He and Prue exchange a brief glance. After the witch hunters are gone, Piper begins to search for the time portal, "where's the damn vortex?", when three pairs of hands place a sack over each sister's head and drag them away.
Back in the present, Leo and Darryl are trying to ID the demons; neither has seen a Grimlock before. Leo is also trying to re-open the portal that "they" sent, making Darryl wonder even more about who and what Leo is. Leo thinks they'll be too much for Darryl to handle and tries to get him out before they unfreeze, but Darryl will have none of it. The Grimlocks unfreeze and Leo and Darryl run for the attic. Darryl empties his pistol into the Grimlocks, incapacitating them. Unfortunately for him, the bullets had no lethal effects on the Grimlocks, as they begin to rise up from the ground.
The sisters find themselves in a cave with several women. One of them, Eva, curtsies to them. She reveals that she is a witch, and that the other women are members of her coven. They are told that the current year is 1670, and they are in colonial Virginia. The other witches give them contemporary clothing. The sisters were brought here to rescue Charlotte, a woman who is giving birth to a magical baby on this day. She was kidnapped by an evil witch, Ruth Cobb, who wants to raise the baby as evil and the only way to stop her is to have Charlotte deliver the baby in their protective circle. The sisters were brought here because "they" thought only the most powerful witches of all time could save Charlotte. Piper wonders how Eva's coven could bring them through time, but not set Charlotte free. Eva reveals that they were brought here through the power of All Hallows' Eve, a most sacred day when a witch can tap into the source of all magic. Prue pulls her sisters aside to talk. The sisters realize "they" won't let them go back, unless they get the baby out of Ruth's clutches by midnight; apparently, that's what Leo was trying to tell them. Eva has prepared a potion that will knock out Ruth's guards so the sisters can free Charlotte.
At Ruth's house, a party is well underway. Eva tells the sisters that while the guests think it's a Halloween party, Ruth is actually trying to tap into dark magic. Piper and Phoebe recognize the witch hunters who chased them earlier; they're working for Ruth. Eva warns the sisters that Ruth's house is guarded by powerful talismans. Phoebe isn't worried; talismans aren't that powerful in the sisters' time. Phoebe moves toward the house, and the talisman sends all four witches flying, alarming the people in front of the house. Eva thinks Ruth tapped into today's power. A guard spots them and shouts an alarm. Prue tries to fling him back, but nothing happens. Piper tries to freeze them, but can't. A gunshot grazes Eva's arm and the four witches run into the woods.
Ruth watches the commotion from her window. Charlotte is having contractions. Cole, disguised as a typical Virginia gentleman, has also traveled through time, and is aiding Ruth. It turns out he made Ruth's talismans even more powerful than normal.
Eva thinks the sisters are frauds, but Prue suspects since they technically don't exist yet, their active powers don't exist either. One of the other witches is about to cauterize Eva's wound, but Piper tells them there's a better way; sterilize it with soap and clean cloths. The sisters think that they can tap into what magic exists in this time, since they were born magical. Eva doesn't think there's time to teach them, but Phoebe tells them they're quick studies.
Leo consults the Book of Shadows, while Darryl stands guard over the attic door. Leo finds the Grimlocks in the Book, and copies the vanquishing potion. The Grimlocks lurk outside; one, peering through the keyhole, starts to strangle Darryl. Leo orbs him to the kitchen and the two begin to prepare the potion.
Charlotte's contractions are closer together. She begs Cole to let her go, but Cole says someone else will only take her right back. Ruth reads tarot cards and finds three good witches, from Cole's time, are after the baby. Cole knows who the three are.
Eva gives the sisters a crash course in 17th century witchcraft. She hands each one a totem; it's a reminder of the wisdom and power of women. She puts a conical hat on a skeptical Phoebe's head; it helps focus energy. A sliced apple contains a pentacle, and with a laurel leaf can block evil. Masks hide one's face from the demons that walk freely on All Hallow's Eve. A broom, by sweeping east to west, removes evil from one's path. Phoebe sweeps warily, and feels a spark come through the broom. Eva sends her fellow witch Sally with the sisters as they go back to Ruth's house.
The festivities continue in front of Ruth's house as Ruth and Cole step outside. Sally hands Phoebe a small jack-o-lantern just before departing. As the masked sisters join the festival, a man with an Irish accent offers to show Phoebe the first letters of her true love's name. Cole joins them and Phoebe drops a slice of apple peel into a bucket of water; the peel shows a C. A man bumps into Phoebe and she drops both her mask and her jack-o-lantern. Ruth recognizes her and points her out as a witch. Prue and Piper try to rescue her and are found out as well. The witch hunters grab the sisters and hang them from nooses on a tree. Three horses gallop away from under the sisters, hanging them.
After the witch hunters are gone from the hanging tree, Micah returns and cuts the still-living sisters to the ground; he had run the ropes to the waist, a trick he had learned from the French. He tells the sisters that he rides with the witch hunters to undo their work.
Leo prepares the potion. Darryl wonders if the Grimlocks are watching them, and Leo thinks they are; it explains why they haven't attacked yet. Trick-or-treaters ring the doorbell. Remembering that Grimlocks steal kids' sight, Darryl offers to bluff the trick-or-treaters away. Leo offers to go instead, but Darryl suspects a trap. Darryl gives all the candy to the kids at the door to make them go away. On his return, the Grimlocks attack and steal Darryl's sight, but he blinds them with Prue's camera, incapacitating them.
The sisters return to Ruth's house. Phoebe doesn't know how they'll get past the talismans, but Prue remembers what Eva said about using the magic all around them. She hands Phoebe a broom to sweep away any evil around them. Piper grabs some lavender for protection, and Prue makes a totem out of some wheat. Phoebe sweeps, and the talismans before the sisters turn blue and fall to the ground. The sisters see several witch hunters grab Micah; apparently he's been outed as a double agent. As they can do nothing for him, they do what Micah would have wanted them to do—find Charlotte.
Prue and Piper enter the house and find Charlotte in a world of pain. Charlotte does not believe them at first, but Piper uses acupressure to relieve Charlotte's pain. Prue and Piper help Charlotte sit up and just then, her water breaks.
Cole kills Micah just as Ruth runs over; she suspects someone might be after Charlotte. Cole, however, thinks the sisters already managed to get Charlotte out, but knows where they're going.
The sisters and Charlotte go to the round stone altar. Charlotte's labor continues into the night. Phoebe and Prue rush to improvise a protective circle while Piper delivers the baby. Phoebe scatters rosemary around them while Prue slices apples. Prue and Phoebe bless the apples, as the witch hunters ride up. They then throw the apples in different directions, forming a protective shield. The shield wards off the witch hunters, but not the bullets from their pistols. The baby comes out; it's a girl. Phoebe decides to intimidate the witch hunters: she puts on a conical hat, mounts a broom sidesaddle and rides it into the air toward the witch hunters, cackling along the way. The witch hunters, spooked, retreat. Cole and Ruth watch from the distance. Ruth looks defeated, but Cole believes time is on his side. He opens a portal and jumps through it. Phoebe proudly rides against the full moon while Prue and Piper look on.
Charlotte promises to tell her baby daughter of the three witches who helped her, and names her daughter Melinda Warren. Phoebe realizes they just helped deliver the founder of their line. The time portal opens again and the sisters return to the present at the stroke of midnight. Leo orbs in from behind and throws a potion at one of the Grimlocks, vanquishing him. He's about to throw the other potion, when the remaining Grimlock strangles him. The potion shatters on the ground. At that moment, the sisters return through the portal. Prue flings the spilled potion onto the remaining Grimlock, vanquishing him as well (and repeating the climactic scene from Out of Sight). Darryl is blind, but Leo heals his eyes.
The sisters and Leo go to P3, the sisters still wearing their 17th century clothing. They bump into a man who strongly resembles Micah, but whose name is in fact Mitch. Phoebe finds Cole dressed as an angel.