Complete story — includes the ending
Phoebe has decided to take a hiatus from men. Piper seems to think Agent Murphy and the government are hiding something from the sisters. She and Paige discover that an experiment with a captured demon created a deadly virus that is infecting the magical community, including Billie. The virus initially doubles a magical being's powers but then kills them. An upper level demon wants to access the power doubling but avoid the death. Eventually the witches destroy the virus by allowing it to infect them so they are more powerful and finding 'patient zero' who was not affected in the military experiments. His blood has the anti-virus to facilitate a cure.
Sources and content license
Source and revision history · Adapted from Wikipedia contributors, Charmed season 8. HTML formatting and reference markers removed. · Content license