This episode opens up with a flashback to a rather essential series of events that involve the three main characters. Don't get your hopes up in terms of exposition- we're given the background but not any sense of how these events in the past relate to the present day. If the antagonistic presence is any relation to the current increase in ghost related mysteries, there's no obvious connection between these plot threads in this episode.
Though there is a definite change in tone. The vengeful presence this time is a migrant worker. And not a passive one either. Whereas previous ghosts were content to just let Cheo Yong slowly get around to solving their problems of afterlife justice, this one makes an active effort to murder people. Yes- now this is a good use of the drama's setting and backdrop. Not a job for normal detectives, but ones who have some understanding how ghosts think