A staircase leading to a schoolgirls' dormitory usually has 28 steps, but sometimes a 29th step appears. Any wish you make while standing on this step comes true, even if it must come true in the most horrific way possible.

A string of brutal murders targeting pregnant women mirrors the crimes of convicted serial killer Shin Hyun, who remains behind bars. Detectives Kim Mi Yun and Kang Tae Hyun take on the case, suspecting that Shin Hyun may be manipulating the copycat killings from prison.