“Sirius” centres on the identical twin brothers Eun Chang and Shin Woo. When they were teenagers, Eun Chang was a bright and popular boy, but he ended up in prison because of Shin Woo. Since then, his life has changed completely. Meanwhile, Shin Woo has always felt inferior to his brother, and his feelings towards him became even more complicated following his imprisonment. Shin Woo is now the chief detective of a police investigation team. He mainly deals with drug investigations. Eun Chang works as a delivery boy in a hostess bar. A conspiracy is hatched by Ko Seok Min, and the twin brothers swap places. Eun Chang now works as Shin Woo at the police station. Shin Woo is devastated that his brother has stolen his identity and begins to take steps to reclaim it. Meanwhile, Ko Seok Min proposes a deal to Eun Chang.