After Phoebe has a premonition about an evil warlock killing Prue to obtain her powers, Prue decides to cast a spell to multiply her powers. However, it doesn't turn out like she expected and as a result, she makes multiple copies of herself. As Piper and Phoebe try to find the best way to warn Prue not fight the warlock on her own, Andy gets some rather surprising news from the medical examiner. Prue and Piper are surprised to find out Phoebe has signed up for a self defense course.
Spoilers ahead. Coverage follows the scope labeled below.
Complete story — includes the ending
When Phoebe has a vividly disturbing vision of Prue being stabbed to death, it coincides with a lord of war named Gabriel coming to town in order to kill the eldest witch-sister as he had done to the sisters' great-great-great-aunt. Prue casts a spell to further develop and strengthen her powers, but ends up making two clones of herself. Her clones are killed off, but working with her sisters, she manages to vanquish Gabriel.