Season 4 brings big changes in the lives of the Halliwell sisters. As they face the loss of a sister, Paige Matthews arrives - half sister to the Halliwells. As Piper and Phoebe cope with the death of their sister, they learn to accept Paige and teach her the ways of witchcraft all while perfecting the use of their own growing powers.
S04E01
Mourning the death of Prue, Piper and Phoebe must now come to grips with the loss of their oldest sister, and the loss of the Power of Three. However, The Source discovers an unknown sister - the daughter of Patty and her whitelighter Sam, who had been kept hidden, Paige, the now-youngest Halliwell can restore the Power of Three and reunite the sisters' strength as witches.
S04E02
Mourning the death of Prue, Piper and Phoebe must now come to grips with the loss of their oldest sister, and the loss of the Power of Three. However, The Source discovers an unknown sister - the daughter of Patty and her whitelighter Sam, who had been kept hidden, Paige, the now-youngest Halliwell can restore the Power of Three and reunite the sisters' strength as witches.
S04E03
Paige takes the Book of Shadows into her work to cast spells which help her co-workers. Meanwhile, Piper, who is filled with anger over the death of Prue and the recent actions of Paige, is possessed by a member of a supernatural band of vigilantes known as the Furies.
S04E04
While making a potion, Paige accidentally switches bodies with Phoebe. Meanwhile, when an apprentice ninja kills his master, the sisters must find a way to vanquish him, while learning to control their switched powers.
S04E05
Piper, Phoebe and Paige are shrunk to a height of five inches when they walk into a trap set by a demon named Gamil.
S04E06
Paige accidentally summons a medieval knight, who believes Paige is the love of his life. However, the knight is under the influence of an evil sorceress.
S04E07
The Source sends Piper into a deep coma, where she perceives an alternate reality. Phoebe and Paige must find a way to return her to reality and save her from giving up her powers while she is delusional.
S04E08
Cole must face his true demonic nature when he is faced with another demon who is mistaken as the murderer of local witches who belong to the same coven. Meanwhile, Cole proposes to Phoebe, and Piper and Leo consider their future involving children.
S04E09
The Halliwell sisters must find a way to release Muses which have been abducted by a warlock who is attempting to build an evil faction in the absence of The Source.
S04E10
With Leo as her guide, Paige goes back in time to her teen years, in an attempt to resolve her feelings about the accident that killed her parents. Meanwhile, Piper must prevent ghosts, who have inhabited Phoebe's and Cole's bodies, from fulfilling their mission.
S04E11
While Phoebe performs jury duty in a murder case, she is hit with a premonition about the real killer, and must convince the rest of the jury that the defendant is not guilty without exposing magic. Meanwhile, Piper, Paige and Leo try help Phoebe find the real murderer, but they stumble upon a gang of demons involved and they must solve the crime and keep Paige's friend out of danger before Phoebe gets thrown off the jury.
S04E12
Wanting to protect a ten-year-old orphaned boy who is a firestarter, Piper and Leo try to hunt down the demon before he can deliver the kid to The Source. Meanwhile, Phoebe is given Gram's wedding ring by Cole, but to their surprise the ring has been cursed to transform the wearer into a traditional 1950's suburban housewife.
S04E13
The Source breaks an age-old agreement between good and evil by stealing The Hollow, an ancient vapor which he uses to absorb Piper & Paige's powers. Meanwhile, Phoebe must allow Cole to help them, despite her having a premonition involving Cole sacrificing his life to save her from evil, but there may be more to the premonition that Phoebe just can't see.
S04E14
Phoebe develops a case of cold feet over marrying Cole and casts a spell which brings a young innocent Phoebe and an old cynical Phoebe to the Manor to help her make a decision. Meanwhile, while Cole is horrified to find that The Source is now taking over his entire being, The Source's chief rival, who believes The Source is dead, is convinced by The Seer to kill The Charmed Ones in order to earn the allegiance of the entire underworld.
S04E15
As Phoebe prepares for her wedding day, she is completely unaware that the Source has taken over Cole's body, a plot that will likely ruin the big event. Meanwhile, when the Seer tells the Source that if he can marry Phoebe in the ""dark way"", it will insure that their future son will be the most powerful, evil being ever.
S04E16
Amongst newlyweds, Phoebe & Cole and already-married, Leo & Piper, Paige begins like a fifth-wheel but she continues her suspicions about Cole. Meanwhile, the Source plots to impregnate Phoebe with his evil spawn.
S04E17
When two ghosts from Leo's past return to seek revenge, Leo faces his demons by submitting, causing Piper's life to be threatened,leaving Paige to deal with the situation. Meanwhile, Cole tries to convince Phoebe they need a home of their own.
S04E18
A vampire queen tries to dethrone Cole as ruler of the Underworld and attempts to turn Paige against her sisters. Meanwhile, Phoebe begins to feel under the weather.
S04E19
Phoebe tells Piper and Paige that she is pregnant, and that Cole is the father. Meanwhile, Piper and Paige team up with a wizard to stop the coronation of the new Source, unaware that it is Cole and Phoebe is soon to be his Queen of the Underworld.
S04E20
Phoebe accepts her new role in Cole's life, but she still sets out to save an innocent after she has a premonition and even seeks her sisters' help in protecting the man. Meanwhile, Piper's heart doesn't seem to be in it as she prepares to defend her family against any new threats from the underworld.
S04E21
The Seer plans to steal Phoebe's unborn baby so she can raise the child to become the next Source and prevent the throne from passing on to another demon. Meanwhile, the baby begins to take over control of Phoebe's body, which proves dangerous to Paige.
S04E22
When the Angel of Destiny offers the sisters a chance to relinquish their powers and lead normal lives as a reward for vanquishing the Source of All Evil, their decision is put on the back burner, while they try and avoid an FBI agent who has them under surveillance and deal with Cole's calls for help, who is trapped in another realm, holding onto his love for Phoebe.