Prue and Piper bring a doctor to the manor, to protect him from a powerful demonic assassin named Shax, who was sent by The Source. When Shax breaks into the manor, he throws Prue and Piper through a wall, causing them to almost die.
The new Source and his queen have to prove that they are truly evil by killing Piper and Paige in order to prevent a civil war breaking out in the underworld.
In his twisted attempt to win Phoebe's heart back, Cole casts a spell that alters reality, which eliminates Paige as a Halliwell and destroys the Power of Three.
The Source breaks an age-old agreement between good and evil by stealing The Hollow, an ancient vapor which he uses to absorb Piper and Paige's powers.
Zankou has stolen the Book of Shadows, and the Charmed Ones start the final battle to stop him and retrieve the books... and eventually even retrieve their lives.
After Prue, Phoebe, and Piper learn that Cole is the demon that has been trying to kill them, Phoebe faces the tough decision of killing the man she loves or defying her sisters by letting him go free.
Phoebe has a vivid premonition foretelling her own death - burned at the stake for killing a man with her powers - in the year 2009. To prevent her execution, the sisters travel to the future.