Seven friends. One secret.

Hye-jin's homecoming should have been a joyous occasion. She was especially happy to see her childhood friend again, the shy Eun-ju. However, when a secret is revealed, harsh words are exchanged. These words deeply affect Eun-ju and,in the next scene, we see her plummeting from a 30-story building. In a flashback provided by Seon-ae, we learn that the ghost of Eun-ju is hunting down all of Hye-jin's friends and killing them. Is this possible or is a more worldly force at work? What is this mysterious tape that everyone is asking about?