This is a summary based on our understanding of the series.
Please also note that this summary contains spoilers.
Na Bong-sun can see ghost. She’s normally very weak as she is always sleepy. She was possessed by Shin Soon-ae who was murdered, who is now a ghost that holds a grudge. At first, she thought the grudge was because she was still a virgin; so she started seducing the Chef (Kang Sun-woo) using Bong Soon’s body so she can lose her virginity. Both Bong Soon and the ghost fell in love with the Chef.
Soon Are discovered that her grudge was being suddenly murdered by Officer Choi, who ran over Chef’s sister. Officer Choi was possessed by an evil spirit.
Soon Ae resolved her grudge and went to heaven, while Chef and Bong Soon became lovers.