Swimming instructor, Young-eun is a single mom raising her 7-year-old daughter, So-hyun. However, a series of tragic events happens as So-hyun’s puppy falls from the apartment and dies, and So-hyun…

A dangerous romance between the Joseon version of a widow hero with a mask and an uptight officer begins.

A demon Jeong Gu-won is superior to humans in every way, but when he loses his powers, he will have to work with a chaebol heiress Do Do-hee to recover…