"The Enemy Within" is a thriller that revolves around former counterintelligence agent Erica Shepard. Shepard, who once betrayed her country, is now one of the most hated people in America and is currently in prison. However, her knowledge becomes essential to the FBI in their fight against a new espionage threat that jeopardizes national security. Striking a deal with the federal authorities, Agent Shepard is granted her freedom, but in return, she must help capture the new traitors of the United States.