Following Prue's death at the end of "All Hell Breaks Loose" season 4 brings the arrival of Paige Matthews - half sister to the Halliwells. The girl's mother Patty had a love affair with her whitelighter Sam and discovered she was pregnant. Knowing she would never be able to keep the baby she gave her child to a local church so she would be given to a kind family.
Most of the first half of the season sees Piper and Phoebe coping with their sister's death, learning to accept Paige and teach her in the ways of witchcraft while learning best how to use their own expanding growing powers which they'd received towards the end of the prior season's episodes. They also focus on destroying The Source once and for all. Phoebe and Cole go through many difficulties in their relationship, such as Cole finding his place once he becomes human. The Charmed Ones must also deal with the new positions they find themselves in; Paige goes from being an only child to having two siblings as well as trying to fill the shoes of Prue, Piper must deal with becoming the oldest sister and head witch giving her more responsibility and Phoebe, who previously had been care-free, becomes the middle sister and must mediate between her two sisters, as well as starting her first full-time job as an advice columnist.
The second half of the season finds Cole fighting once again with the evil inside him, only this time it is The Source. Although he plans to rebuild the underworld and destroy The Charmed Ones, the human inside plots to convert Phoebe and have her rule by his side as his Queen. We are also introduced to The Seer who has an evil agenda of her own.
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