Signals for hide-and-seek □1○1△2. Seong Soo, a successful businessman who lives with the perfect family in a luxury apartment, has secrets and mysophobia about his one and only brother. One day, he goes to see his brother after a phone call about him missing and sees weird symbols all over the house and he meets Joo Hee who knows his brother. "Please tell him to stop looking at my daughter". Joo Hee read morelives alone with her daughter but lives in fear of someone watching them. Seong Soo looks around carefully at the old apartment and realizes the symbols mean gender and numbers of people. "Someone else is living in my apartment with me!". Seong-soo returns to his from his brother's and notices a familiar symbol written next to the bell of his house. A missing brother. Hide and seeks codes. A shocking truth for two different families and the struggle to save their families starts now.