整日奔波處理許多個案的社工師李淑芬（楊丞琳飾），某天接獲通報到一樁虐童案件，正盤查女童母親林美華（高慧君飾）時，突然接到女兒雅婷下午失蹤於校園的消息，心急如焚的淑芬查看學校監視器後，竟發現雅婷跟着一名穿着紅衣,身影詭異的小女孩離去，這個小女孩是誰？她們要去哪裏？循着線索，淑芬隨着救難隊在山區的廢棄醫院發現疑似雅婷的蹤影，但找回的卻是失蹤已久的廣播主持人沈怡君（許瑋寧飾）。無計可施的淑芬只好先將精神不穩定的怡君帶回家，希望能從中問到女兒的下落，沒想到帶回家的可能不只是怡君…。

A mother goes in search of her missing teenage daughter after her sudden disappearance. She is told that her daughter was last seen in the company of a girl in red, leading the mother to attempt to unravel the mystery behind the girl.