Michele is 30 years old, married and seemingly happy. One night, whilst stopping at a petrol station, he allows himself to be seduced by a young street prostitute. Back home, and feeling guilty for having lost his wedding ring during the sexual encounter, Michele begins to harbour overwhelming feelings of guilt towards his wife Stefania. The following morning, near the cottage where Michele had the encounter, the brutally murdered body of the young prostitute is found lying in a pool of blood. And whilst Michele, tormented by the confused memories of the previous night, begins to lose his mental balance more and more, at the very same moment an experienced police inspector begins to investigate the wedding ring found just a few steps away from the murdered young woman. Thus begins his search for the killer, and soon his life becomes intertwined with that of the unfaithful young man, leading him to question just how deep the evil that lies within human beings can be.