Mariko is a tomboyish female detective. She goes with her boyfriend, Detective Muraki, to mediate a lovers' quarrel, but her carelessness leads to the death of the couple that Muraki was fighting with, and Muraki's gun goes missing, escalating into a major incident. Though she herself is injured, Mariko takes responsibility and is suspended. However, her suspension ends suddenly. One day, her new partner, Mika, brings Mariko a case. The case is a series of murders involving Muraki's lost gun! Thinking of Muraki, Mariko becomes absorbed in investigating the case, while Mika tries to skillfully take the reins. As they investigate the case, one woman's sad past comes to light...