When a normally meek Bay Area insurance agent suddenly turns into a voracious, homicidal maniac with an uncontrollable appetite, doctors quickly determine that the cause must be a brain parasite that can only be extra-terrestrial. Now, San Francisco Police Detectives Karen Hall and Yuri Markov are on a mission to end this wave of violence before more citizens become infected. But at every turn their investigation seems to be hindered by shadowy federal agents with a hidden agenda. Can they stop this reign of terror before one of them becomes the next Symbiote?