The help of the Charmed Ones is enlisted by Agent Murphy when a demon escapes from the government's custody. They discover that a government-created virus is spreading amongst magical beings causing them to "hulk out." After Billie is scratched by a demon and becomes infected with the virus, Piper and Leo race against time to find an antidote to save her life. The sisters realise the only way to save Billie is to become infected with the virus and turn into "hulked out" versions of themselves. Meanwhile, Paige is put in charge of watching a baby when one of Henry's parolees is busted. Phoebe reflects on her failed premonition about having a baby.