Keith Cafferty spends his monotonous days working at a pharmacy, creatively dispensing medication to his ill patients. After work, he comes home to his girlfriend, Sheila, who is becoming strangely and inexplicably sick. Keith tries to help her through rational analysis and medicine, only to end up mimicking her symptoms. The more dogmatic his regimen becomes to make them better, the worse things get. The two become more and more similar in their physical appearances and behaviors, until they are forced to embark on a journey together that will either lead to their destruction or salvation.