A female detective investigates the cause of a high school girl’s death and uncovers a disturbing truth.

On the afternoon of the day before her school trip, Se-mi wakes up from her strange dream and heads to her Ha-eun. It was because she felt like she had to convey the feelings she had been holding back for a long time today. However, unlike her overflowing heart, the two keep falling apart.

Beyond the invisible boundary, reality twists into nightmare. A seed of doubt takes root—growing into unstoppable fear. In the shadows, someone is watching. Curiosity becomes your greatest danger… and your darkest transformation. Enter the Forbidden Zone—a place no one should ever cross.

Seung-soo visits Min-ji's funeral home, his younger sister's friend.