Three sisters - Prue, Piper and Phoebe Halliwell - reunite in their ancestral home, Halliwell Manor. When the youngest sister, Phoebe, ventures into the previously-locked attic, she recites a passage from an ancient book which unlocks their dormant powers to transform them into The Charmed Ones - the most powerful witches ever to exist. Now they must vanquish evil and save innocent lives while living their own lives as normal women in the real world. Life isn't so easy when you're Charmed.

In Charmed Season 4, half-sister (and half-Whitelighter) Paige replaces the dearly departed Prue in The Power of Three.
In Charmed season 8, a life-or-death decision forces the sisters to fake their deaths and take a young witch named Billie into their care to help them fight the evil forces that once threatened their existence so that they could maintain the 'normal' lives for which they had spent the last 7 years fighting to regain.