In order to get Billie to fight the Charmed Ones alongside of her, Christy and the demonic world resort to deception in order to get the magical community to think the sisters are no longer using their powers for the greater good, and as a result, need to be stopped. As a result, Piper, Phoebe, and Paige have to hide in the underworld in order to come up with a plan to fight back. Meanwhile, the demons working with Christy reveal that the upcoming battle will not only destroy the Charmed Ones, but also Billie and Christy.
Spoilers ahead. Coverage follows the scope labeled below.
Complete story — includes the ending
Christy has now managed to convince Billie that the Charmed Ones are too self obsessed to help the 'greater good' so when Paige, Phoebe and Piper attempt to involve the rest of the magical community, Christy and Billie cast spells on the sisters that turn all the leprechauns and other creatures against the Halliwells. With their support, Christy and Billie then directly attack the Charmed Ones who attempt to escape to Magic School but find that it has been blocked from them and so end up in the underworld...