Sometimes it can be hard for a teacher to forget a student in more ways than one! Jong Goo (Kim Jeong Hoon) is a high school teacher who is distraught after one of his students, Yeo Ri (Song Ji Eun), disappears. Yeo Ri came back into Jong Goo’s life as a ghost, and another student, Ha Na (Lee Jin), is the only person who can see her. Can fellow teacher Hae Joo (Lee Jung Bin), who has a crush on Jong Goo and Ha Na help Jong Goo investigate what happened to Yeo Ri?