Simon (Cavan Clerkin), an unhappy and unfulfilled office worker, decides to turn his life around by joining a local gym. There, he meets Terry (Craig Fairbrass), a highly aggressive, manipulative personal trainer who takes Simon under his wing. As Terry pushes Simon to transform his body, he steadily moves into Simon's home, taking over his personal life and turning his residence into a chaotic hub of drugs, prostitution, and wild parties. Simon's relationship with his long-term partner collapses as Terry's toxic influence completely consumes him.