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.

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.

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.

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.

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.

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.

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.