When a man is found at the base of a mountain with his skull crushed, it looks like he slipped, or did he commit suicide, or was he pushed? Well it falls to detectives "Jang Hae-joon" (Park Hae-il) and his young sidekick "Soo-wan" (Go Kyung-Po) to get to the bottom of it. They are suspicious enough, but the only realistic suspect is his younger widow "Song Seo-rae" (Tang Wei) - but she has an alibi. She looks after ageing grannies and they swear that she is the milk of human kindness. Gradually, the older policeman begins to obsess a little about her. He stakes out her apartment at all hours, ...