Song Yoon-ah plays the role of Kim Yoon-jin, who was a doctor and became a full-time housewife in order to focus on her children's education. She met a surrogate mother for the entrance examination through her husband's introduction, and the two formed a deep friendship. Kim So-yeon plays the role of the mysterious exam nanny Risa Kim. She runs a homestay for children who come to the United States for training, and is an exam nanny who gives them warm care. Kim Tae-woo plays the role of Han Jae-yeol, the husband of Kim Yoon-jin (played by Song Yoon-ah), the police chief. He is gentle, likable, and treats prisoners 180 degrees. Song Jae-rim plays the role of the powerful policeman Xia Zhengwan in the play. He is tall, handsome and honest. He takes a step back and observes everything, but once he starts doing it, he will move forward bravely and do it without hesitation. The play is a female suspense thriller that tells the story of a family that hides the secret of their child's death, and a mysterious exam nanny [parents whose children attend prestigious universities, who are paid and entrusted by others to help tutor other families' children for the college entrance examination] who lives in the family.