After discovering that a demon is trying to rid himself of his humanity by killing all his remaining human family, Paige decides to cast a spell from all forms of death from happening. As a result, the Angel of Death forces Piper to help right what happened and return order to the world by turning her into a collector of souls.
Spoilers ahead. Coverage follows the scope labeled below.
Complete story — includes the ending
When a demon, Sirk, tries to destroy his human half by killing off his remaining blood relatives, Paige casts a spell that inadvertently blocks all death from occurring. Annoyed that he now has a backlog of work, the Angel of Death insists that the Charmed Ones help him clean up the mess and "kills" Piper so she can help him restore the Grand Design. Meanwhile, Phoebe earns back her power of premonition.