When an Earthquake hits San Francisco, Prue, Piper, and Phoebe have to call the gas company to repair a leak in the basement. However, once the repairman arrives, he is possessed by the woogyman – a shadow demon previously defeated by Grams. After he banishes Prue and Piper from the house, he possesses Phoebe and in order to defeat the demon the sisters have to find a way to banish it again and save Phoebe.
Spoilers ahead. Coverage follows the scope labeled below.
Complete story — includes the ending
Phoebe is corrupted and turned against her sisters by the "Woogyman", an extremely powerful entity that is released following an earthquake. Under the orders of the Woogy, she corrupts others as well, including one of Claire's associates from the Auction House when they visit for a work mixers. Before Piper and Prue can be enslaved, Phoebe recites the vanquishing spell after having a past vision of Grams defeating the Woogy from a picture frame when she was younger.