 The Charmed Ones find themselves stuck in the Underworld attempting to restore the reputations that Billie and Christy tarnished. Piper sees Leo s ghost and he gives his approval for the sisters to team up with the demon Nomed. Billie, Christy and the Charmed Ones realize separately that they must conjure The Hollow, the most powerful force known to man, in order to defeat one another, leading to a devastating battle.