The Source possesses the body of Paige Matthews's boyfriend to seduce her to the evil side. Meanwhile Paige acknowledges her power with the support of Phoebe and Piper. Inspector Cortez puts the Halliwell sisters under surveillance, and Darryl, Cole and Leo are not able to convince him that the sisters are the "good girls". Paige helps Leo to save Cole with her whitelighter ability.
Piper is full of anger for the death of Prue and vanquishing as many demons as possible, jeopardizing her, Phoebe and Cole's lives. Paige "borrows" the Book of Shadow without permission of her sisters to cast spells to help her colleagues in South Bay Social Services office. When Piper, Phoebe and Cole fight against The Furies, Piper inhales a smoke released by one of the demons. Her anger is magnified and Piper is transformed in one The Fury.
Phoebe and Paige must work quickly before Piper is tricked into giving up all of their powers when The Source taps into her brain, altering her perception of reality and placing her in a mental institution.
Paige brings a baby-robot and gives it to Piper and Leo to see if they can conciliate having a baby of their own and vanquishing demons. Meanwhile, the Halliwell sisters are chasing a demon that kills witches from the same coven with his Athame, a weapon used also by Belthazor. When they face the powerful demon, disguised as the District Attorney Sykes, Cole needs to leave his human nature and unleash his true demonic nature at all to vanquish his replica, paying a price for his action.
Paige has an unresolved trauma since she blames herself for the death of her parents in a car wreck. Leo summons the spirit of time Clyde and goes back to the past guiding Paige in the 90's to revisit the tragic day of the accident and resolve her guilty complex. Meanwhile, the spirits of a couple of criminals possess the bodies of Phoebe and Cole to finish an assignment of fifty years ago.
Phoebe is serving on a jury in a murder case, and she is convinced that the defendant is guilty. However, when she touches the murder weapon, she has a premonition of the real killer, who has a Medusa tattooed in his right arm. Meanwhile, the irresponsible Paige invites her snoopy friend Glen Belland to stay with her in the Halliwell manor, and he finds the Book of Shadows in the attic. While Piper, Leo and Paige try to find the real killer, Phoebe decides to use magic to prove the innocence of the accused to the jury.
Cole proposes to Phoebe again, only now as a 'normal' human being, and accepts Paige's offer to come work for social services, where his zeal to deal with slum lord Alan Yates soon exceeds human boundaries. Meanwhile, Grams' engagement ring turns Phoebe into a traditional 1960's suburban housewife. At social services, Paige notices that a runaway ten year-old named Tyler has a rare magical power, the ability to start fires.
When The Seer foresees the demise of The Source by the Halliwell sisters, he decides to break the covenant between good and evil unleashing the ultimate power, the forbidden The Hollow. He kills the Guardians of The Hollow and uses the dangerous lethal power to absorb the powers of Piper and Paige. Meanwhile, Phoebe has a premonition of Cole sacrificing himself to protect her against a ball of fire, and they try to find in the Book of Shadows means to vanquish the powerful demon and trap The Hollow again.
Phoebe has a strange sensation about Cole, and she casts a spell to know whether she should marry him or not, bringing unexpectedly an innocent Phoebe from her childhood and a bitter Phoebe from the future to help in her decision. Meanwhile, The Source is getting stronger and possessing Cole, who seems to be unable to resist much longer. The greedy demon Kurzon that wishes to assume the position of The Source is advised by the evil The Seer to kill the harmless young Phoebe and destroy The Power of Three. Paige has a personal gain with Carolyn case being promoted in ...
The Seer foresees that the son of Phoebe and Cole will be very powerful, and The Source, who possessed Cole's body, must bring him to the evil side marrying Phoebe in the dark way, i.e., in a cemetery with a dark priest and drinking the bride's blood. Cole sabotages the wedding and The Seer releases a Lazarus demon that resurrects when destroyed unless buried in a cemetery to force the ceremony to take place in a cemetery.
The Seer gives Cole a potion hidden in chocolates so that Phoebe will conceive a son. When Piper and Phoebe save the life of the innocent columnist Karen Young, Phoebe has a premonition and realizes that Karen has been attacked and infected by a ball of light of a demon. Meanwhile, Paige unexpectedly arrives at home and sees Cole using demonic power on Karen. She tells Piper, who does not believe her. Cole sends a demon to infect Paige and destroy her credibility.
After 60 years of searching, two ghosts who fought with Leo in WWII come after him seeking revenge for old wounds. When they turn this wrath on his loved ones and kill Piper, Phoebe and Paige face the horror of losing another sister.
Phoebe is irritated with the lack of attention of Cole and destroys five of his demons in a couple of days. She has a premonition of a demon killing the innocent Greg Conroy, she tells her sisters at the Halliwell manor and together they go to an alley and save Greg Conroy. However, when Phoebe spares the demon, Piper tells that she must take a side and Phoebe decides to stay with Cole. When Cole is pressed in the underworld to kill Greg, Phoebe has to decide which side she should stay: in the evil side with Cole or in the good side with her sisters.
Phoebe's unborn baby begins to show signs of demonic powers as it begins to take control of her body and attack Paige and anyone else who might be a threat to it. Meanwhile, the Seer plans to magically steal the baby and make it her own in order to gain its powers and become the next Source.
While Phoebe feels Cole trying to contact her, the Angel of Destiny comes to the Halliwell manor and proposes to remove the powers of the sisters as a reward for vanquishing The Source. Meanwhile, the FBI agent Jackman bugs the manor and discloses that he knows that the sisters are witches. He proposes to eliminate the evidences if the sisters find a witch hunter that is killing witches. Phoebe casts a spell to meet Cole in a demon limbo.