853 refers to the precinct where Detective Shinnosuke Kamo used to work. But this was before he accidentally shot a criminal in his custody. After that incident, Detective Kamo is reassigned to a smaller, rural jurisdiction. For 10 years, he keeps his nose to the grind, continuing to do great investigative work despite the demotion to a smaller police precinct. Until one day, he is called back to put his detective skills to work again in the 853.