A murder case occurs in Woojin, a town blessed with no crime. Detective Oh Jin Seong, known for being cheerful, joins the investigation team when his younger brother Jin Woo is identified as a suspect in a murder case. Jin Woo is eventually cleared of false accusations, and the culprit is revealed. Jin Seong's performance earns him preferential treatment at the Gangnam Police station, but his brother is suddenly attacked by someone on a rainy night and dies unexpectedly. Jin Seong starts chasing after the true culprit of the murder case while facing his own family's desires and secrets.