Who's That Knocking at My Door?

A young loner named Je Hwi was tormented and bullied by a classmate named Pyo in high school. Now a young adult, Je Hwi begins to open up to his girlfriend Jang Hee. However, a revenge plot he had hatched against Pyo with a stranger he met over the internet, begins to grow way out of control with cruel and unpredictable results.
(Source: AsianCrush.com)