The sisters return from a shopping spree. Prue turns on the TV, but snaps it back off after hearing reports of a street brawl; she's noticed a spike in violent behavior of late. Phoebe has brought home a book full of deep questions and thinks that it might make a great bar game at P3. She finds one: "What if a building is on fire? Do you save five strangers or one sibling?" Prue says "one sibling" without a moment's thought and Piper agrees. Before Phoebe can try one, though, the doorbell rings and Leo is at the door. Paula Cole is playing P3 tonight, and Leo wants to take Piper to an early dinner beforehand. Piper is reluctant, since it's been a while since the sisters have done anything together that isn't magical. However, Prue and Phoebe talk her into going.
Returning from dinner, Piper and Leo are caught in traffic. The man behind them starts honking. In time, he pulls out into the opposing lane and makes a sharp left turn, hitting a pickup truck hauling fruit. The truck driver yanks the car's driver out, and a huge brawl ensues. One guy hits Piper's Jeep with a watermelon. Piper and Leo get out and try to break up the fight. The guy who threw the watermelon hurls another one, but Piper freezes it before it hits her. Piper looks around, and notices a man in a black suit and green tie didn't freeze. He spots Piper and Leo and runs away. Piper chases him, and Leo chases Piper. In an alley, he conjures a horse and then vanishes. In a valley far from the scene, Green Tie is joined by three other men, all wearing black suits and riding horses.
Piper and Leo arrive at P3 just as Paula Cole is finishing a set. They tell Prue and Phoebe of the man in the green tie. The sisters go to check the Book of Shadows.
Green Tie tells his colleagues that a witch saw him. The others decide to set a trap for her so they meet an unspecified "deadline" by 7:00 the next night. Piper and Phoebe are trying to narrow down possible suspects. Prue and Leo walk in; Piper thinks its the Demon of Anarchy. Leo thinks it's too risky to go after a demon without knowing who he is and what he wants. The sisters, however, think they can't wait to find out everything about this particular demon if he's causing so much havoc in the city. While Piper mixes a potion, Prue calls Darryl, who reports chaos all over the city; there are fights and struggles in the police station. She asks for the current hot spot, and Darryl directs her to it.
The sisters arrive to find a full-blown riot underway. Piper spots Green Tie again and this time all three sisters pursue him. Red Tie grabs Prue and the other three start chanting; Piper and Phoebe start the vanquishing spell for the Demon of Anarchy at the same time. Piper throws a potion, and to their surprise, both Red Tie and Prue disappear into a portal. The other horsemen vanish. Piper is distraught; she thinks they just vanquished Prue. However, Phoebe thinks they merely sent her somewhere else.
The other horsemen appear at something resembling a corporate office, with Omega as the logo. They turn out to be the Four Horsemen of the Apocalypse--and they're due to cause the end of the world by 7:00. Yellow Tie is worried that Red Tie is dead, but Green Tie reminds them that the Source is the only one that can kill them. Black Tie blames Green Tie for getting witches on their trail. Yellow Tie points out that if they miss the 7:00 deadline, the Source will kill them and choose four new Horsemen. Black Tie points out they need Red Tie, who is really War, in order to set nations fighting against each other. All around the office, large screen TVs show scenes of strife.
Piper and Phoebe return to the attic. Leo has been through the entire Book and found nothing. Piper feels a chill; she felt Prue's presence in the room. Phoebe calls to Prue, but all she can do is spell HELP on the Spirit Board. Phoebe feels a chill as well, but evil and cold. A white bubble appears in the air with Prue's face in it, pursued by a red bubble with War's. Leo goes to his "bosses" to ask who the four suits are.
Back at the Horsemen's headquarters, one of the TVs starts showing one scene of war after another, and finally a scene of static. War tells the others to ask the Source how to find the witches so they can free him.
Leo orbs in with a message from the Elders. They've talked with the bosses of the "suits," and the only way Prue and War can be freed is if Piper and Phoebe work with the suits. Leo suspects a trap, but Piper and Phoebe are determined to get Prue back. Piper and Phoebe meet the "suits", and after a bit of bickering Piper shakes with Green Tie, to the crash of thunder.
Piper and Phoebe bring the suits to the manor, where they think they'll be safest. They disagree on where they had been standing, and finally Green Tie places the five markers in the correct positions. The two witches and the three "suits" had formed a pentagram. Black Tie goes back to the office, and Leo decides to orb after him. Piper mixes the potion again.
Phoebe has uneasy conversation with Green Tie. He explains the chant that they had used, a chant "to destroy the common witch". He offers a translation, but Phoebe interrupts him, though Green Tie continues to flirt, to Phoebe's discomfort.
Leo, at Omega, punches a random employee and puts on his shirt and tie. He skulks about, and spots the names of the Horsemen. Red Tie is War, Green Tie is Strife, Yellow Tie is Famine and Black Tie is Death.
Piper notices Famine's Omega tattoo as she remixes the potion. Piper asks questions, but Famine gives no answers.
The white bubble appears again and Phoebe feels a chill. The Spirit Board moves and spells out IV-H-O- before the red bubble knocks the pointer off. Piper and Famine hear commotion and come in. By reversing their positions and the meanings of their spells, they can open the portal and bring the fourth "suit" back. Famine and Strife return to the office.
The man whom Leo attacked spots him snooping and points him out. Leo orbs away and tells the sisters that they are working with the Four Horsemen. If they free Prue, he says, they'll free the fourth Horseman as well--and bring about the end of the world. They've chosen this date because New Year's Eve 1999 wasn't the actual end of the previous millennium. The millennium actually starts that night, at 7:00. However, Piper and Phoebe still insist on freeing Prue -- one sibling over five strangers.
Phoebe and Piper meet the Horsemen just before 7:00. Phoebe shakes hands with Strife and gets a premonition of nuclear explosions. Strife starts chanting. Piper starts the spell, but Phoebe, realizing that Leo was right, doesn't join her.
Strife finishes his chant, and now Piper doesn't join in either. The Source opens the portal anyway, and begins destroying the Horsemen. Phoebe finishes the chant, and Prue comes out. While Prue runs to safety, the Source destroys the Horsemen.
The reunited sisters meet Leo at P3, and Leo offers a thanks from his bosses. He reveals that the sisters' act of selflessness stopped the Apocalypse from happening. Leo leaves the sisters together. The bartender comes up with the book and asks the five-strangers question. The sisters answer "five strangers" in unison.