事业有成的中年男子白成洙(孙贤周 饰)与妻子闽祉(全美善 饰)以及一双儿女户三和秀雅住在一幢高级公寓中,衣食无忧,幸福安逸。这一天,他意外收到一通电话,对方称成洙的哥哥成则失踪数月,下落不明。成则自高中后离家出走,期间履历中留下不光彩的记录。心中怀有隐秘的成洙来到哥哥所在的公寓,发现其房内有许多别人衣物,并且周围住户都对成则谈之色变,而各家门口也都标记了意义不明的记号。未过多久,一名头戴摩托盔的神秘男子袭击了闽祉母子,危险明显向白成洙一家逼近,有着严重洁癖的成洙精神几近崩溃。 豪华敞亮的私宅内,神秘之人悄悄入住,与主人玩起了凶险非常的捉迷藏……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 lives 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.Seong-soo returns to his from his brother's and notices a familiar symbol written next to the bell of his house too.