Phoebe and her sisters eventually learn that The Triad work for an even greater evil, The Source of All Evil who is the leader of the demonic realm known as The Underworld. In the season three finale, Phoebe ventures into The Underworld to save Cole from his dark side, while her sisters face dire consequences in the world above. Prue and Piper unwittingly expose themselves as witches to the world after being caught on camera by a local news crew fighting with The Source's personal assassin Shax. This results in Piper's catastrophic death in the arms of Prue, and Phoebe unable to help them. In order to save Piper's life, Prue orders Leo Wyatt (Brian Krause) to find Phoebe and pass on a deal to The Source to turn back time. The Source agrees, knowing that he plans to double cross her in the end as Phoebe will be immune to the time reset while in The Underworld. Time is reversed to the sisters' first encounter with Shax, however Phoebe no longer answers when Prue calls for help, as she was never sent back. The season ends on a cliffhanger with Piper and Prue left for dead after losing in the fight against Shax. Meanwhile, Phoebe remains trapped in The Underworld. The opening episode of the fourth season (2001–02), "Charmed Again (Part 1)", reveals that Phoebe was rescued from The Underworld by Leo and Cole. However, because of this they arrived too late and were only able to heal Piper of her injuries from the season three finale. Prue's injuries from Shax were too severe and was unable to be saved. Later in the episode, while attending Prue's funeral, Phoebe meets Paige Matthews (Rose McGowan) and receives a premonition of the woman being attacked by Shax. This incident leads to Phoebe and Piper discovering that Paige is their younger half-sister. By the end of the season premiere, Paige helps to restore the Power of Three and avenge Prue's death in vanquishing her murderer Shax. During this season, Phoebe finds herself forced into the role of the middle sister as she attempts to play mediator between Piper and Paige, much like Piper was once for her and Prue. Alongside continuing her Charmed role, Phoebe receives a marriage proposal from Cole, accepting after he becomes stripped of his demon half. Phoebe eventually pens the spell to vanquish The Source, whom escapes a final vanquish by possessing the now human Cole.