The third season of Charmed sees many dramatic changes in the sisters' lives. As Cole/Belthazor moves his way into The Charmed Ones' lives, he becomes conflicted between his duty toward The Triad and his love for Phoebe.
While Piper and Leo are away, Prue and Phoebe must face a series of demons known as Guardians, who protect mortal murderers in exchange for the souls of innocents. After saving Darryl from a Guardian, Prue and Phoebe must testify in court, where they stumble upon an evil conspiracy. Meanwhile, Phoebe falls in love with the new district attorney, Cole Turner.
The sisters must find a way to break a curse which turns a man into an Owl by day and his girlfriend into a Wolf by night. Meanwhile, Prue discovers a way to hold Piper and Leo's wedding without 'The Powers That Be' finding out.
With Piper growing more concerned that Leo will never return, Prue and Phoebe try to save a little girl and a fairy princess from evil Trolls. When Prue and Phoebe need Piper's help, her concern with Leo causes a spell to backfire, placing the girl in danger.
On Halloween, the sisters are pulled back in time to the 1600's to save a witch and her soon-to-be-born child from the hands of an evil witch who wants to raise the child evil. The sisters later discover that this situation may have more personal implications than they first imagined.
Prue becomes increasingly paranoid over attacks from the Triad, and the mysterious threat Belthazor poses. After the house is robbed, Prue is convinced the Triad is launching an attack, when the real culprit is more mortal than all three sisters realise.
Prue begins experiencing the powers of an empath, thanks to a warlock, but she soons loses control. Meanwhile, Phoebe's relationship with Cole becomes turbulent when he tells her he doesn't want to see her anymore.
In an attempt to destroy the Charmed Ones, Cole enlists the help of Andras, a demon who magnifies anger into rage. Meanwhile, when the sisters lose their magic after using their powers against each other, they are left defenseless against attacks from the Triad and Belthazor.
When the sisters discover that Cole is Belthazor, Phoebe must make one of the toughest decisions of her life: either vanquish her boyfriend or keep one of the most dangerous demons known to exist alive.
Prue & Phoebe have their hands full when Piper is possessed by the spirit of an evil witch, on the day of her high school reunion.
The sisters trace a mysterious Ice Cream Van who abducts children, but the evil may not be who they initially suspect. Meanwhile, the girls' dad Victor comes for a visit.
The sisters must stop a warlock from executing his plan to steal specific powers from witches in his attempt to kill every whitelighter in the world.
When Prue discovers that her ex-boyfriend is being led down the path to becoming a demon, the sisters must risk their lives in an underworld wrestling ring to save his soul.
When a shapeshifting warlock tricks Prue into a shot-gun wedding in order to steal the Book of Shadows, Phoebe and Piper are lured to the dark side and begin to enjoy their new evil powers.
When Phoebe feels the pain of an injured American-Indian ghost she sees in a deserted town, Prue travels back in time to the mid-1800s to save the man, and Phoebe, from death at the hands of a local thug.
On the day of Piper's marriage to Leo, Prue's Astrally Projected-self adopts an uninhibited, wild personality that threatens to ruin the wedding and place Prue in jail for Murder.
Prue, growing weary of her battles to save innocents and in fighting off the Angel of Death, is forced to turn her back on a dying soul, and must come to grips with her feelings towards fate and the death of her mother.
While the sisters must deal with the possibility of being separated as the newlyweds plan to move out on their own, they recall a time before they knew they were the Charmed Ones, when the girls were coming to grips with the death of Grams and Phoebe's departure to New York.
A demon turns people into the embodiment of each of the deadly sins, including the Charmed Ones and Leo.
Cole poses as Belthazar to infiltrate an internet organization run by evil, that plans on controlling the world's information flow on the internet. Meanwhile, the sisters must vanquish the warlock posing as the company's manager without exposing Cole's role in the situation.
The evil Brotherhood plots to sabotage Cole's relationship with Phoebe in an attempt to turn him back to evil. Meanwhile, Piper's power develops with some explosive results.
Phoebe has a premonition of a murderous banshee while adding on to the Belthazar section of the Book of Shadows, thus causing her to think Cole is responsible. But when the sisters cast a spell it backfires and turns Prue into a dog, and when Prue gets hit by a car, Phoebe's remorse causes the banshee to attack her, turning her into a banshee.
When the Halliwell sisters are exposed as witches on nation-wide television, they form a pact with The Source to reverse time and undo the damage. However, in the process, one of the sisters makes the ultimate sacrifice, placing the Power of Three in mortal danger.