The Suspicious Housekeeper follows the story of Park Bok-nyeo, a mysterious and emotionless housekeeper who is hired by a grieving father, Eun Sang-chul, to take care of his four children following the sudden and tragic death of their mother. Bok-nyeo is known for her absolute efficiency and her willingness to perform any task requested of her, no matter how bizarre or dangerous, as long as it is not illegal. However, her stoic demeanor and hidden past begin to unravel the secrets of the Eun family. As Bok-nyeo integrates into the household, she becomes a catalyst for change, forcing the fractured family members to confront their grief, resentments, and hidden truths. While she helps them heal and find their way back to one another, the mystery surrounding her own tragic history—and the reason she refuses to smile—slowly comes to light, threatening to disrupt the fragile peace she has helped build.