A group of internet friends rents a beach apartment for the summer, eager to meet in person. They are divided over the suicide of a chatroom member, "Sandmanz," with some thinking he deserved it and others, like Yoo-na, believing he was forced out by lies. Suddenly, a mysterious figure starts killing them, sending emails warning their fates will mirror Sandmanz's. The search for the killer begins as the group is picked off one by one.