Season 1 of Armed Reaction 2021 premiered on January 25, 2021.

Inspector Tai On-na has been happily carrying out her admin duties in managing files. Fate has brought On-na, seasoned armed lady cop Chan Sam-yuen and SDU Prince Mung Hon-sam together. After some case is solved by the trio, On-na’s boss Wai Chin-chiu assigns On-na to Cold Case Special Investigation Unit. Under Hon-sam’s command, On-na and a contingent of police officers with “special characteristics” investigate cold cases that outsiders are not interested in. Hon-sam and On-na keep outwitting each other as Hon-sam is disappointed with On-na. Hon-sam eventually discovers On-na has gun phobia as she was once taken hostage, causing the two of them to fall in love. On-na again runs into Lau Tat-wah , who used to be a tutorial student. However, Tat-wah, who had the misfortune of all his family members being killed, has become a gangster. Driven by emotions and guilt, is On-na capable of regaining her confidence, holding a gun in her hand again and becoming the new iconic “armed lady cop”?