Jo I-na finds her uncle murdered beside a puzzle piece but can't explain her presence. Ten years later, as a criminal profiler, she investigates murders where victims are found with similar puzzle pieces.

Detective Ma Seok-do joins the Cyber Investigation Team to nab Baek Chang-ki, a former mercenary and the head of an online gambling organization.

Seven years after the roundup in Vietnam, Ma Seok-do joins a new squad to investigate a murder case. He soon starts to dig deeper when he finds out the case involves a synthetic drug and a gang of thugs.