Watch The Ultimate Duo (2026) Official Trailer

One case, two suspects

Jae-hyuk was once a star detective in the regional investigation unit, but after losing his marriage and missing promotions, he's now a washed-up small-town cop whose life has completely fallen apart. His new partner is Jung-ho, a rookie detective and former influencer armed with sharp intelligence, ambition, money, and youth. The mismatched duo doesn't click at all, but one day they arrest a thief who stole from a church donation box and discover he's a prime suspect in a Gangnam murder case. However, the case has already been closed with another perpetrator arrested. To catch the real killer, they head to Seoul on a business trip. With prosecutor Mi-ju's promise to support are investigation, they request cooperation from Gangnam Police Station. But their questionable teamwork - or is it team-killing? - puts the case in jeopardy.