The Neighbors

Residents of a small apartment building learn that a serial killer lives within their building. A stepmother feels heavy guilt for not being able to prevent her stepdaughter's murder. The stepmother takes it upon herself to find the killer. Meanwhile, a young girl that resembles the murdered girl becomes the next target of the serial killer.
~~ Adapted from the webtoon "Neighbor" (이웃사람) by Kang Full (강풀).