Eriko Osawa (Yuki Amami), a 40-year-old single former careerist returning from the U.S., is selected to head the “Special Crimes Unit” newly established in the Investigation Department of the Metropolitan Police Department. Eriko was a promising career officer, but after a scandalous incident, she was demoted and sent to the U.S. for training, where she studied for five years at the FBI and other organizations before returning to Japan.