Mi Ju is a part-time music professor with a tragic past. When she was younger, she was an up-and-coming cellist, until she was in a car accident with her rival/best friend, Tae Yeon. After Tae Yeon died, Mi Ju gave up playing the cello and decided just to teach. One day, one of her students threatens her after receiving a bad grade and so begin Mi Ju's problems. She is sent a mysterious cassette tape that contains a haunting cello duet that dredges up some painful memories of Tae Yeon and almost causes her to get into a car accident.
She is distant from her loving family which includes her two daughters, husband and sister-in-law. Her older daughter is mentally disabled and mute, but falls in love with a cello she spies in a window. Mi Ju buys it for her and begins to teach her how to play it. Meanwhile, a new maid moves into the house. She is creepy as hell and is also mute. It seems as though her family was killed in a car crash and she tried to commit suicide numerous times, once by swallowing acid. No more vocal cords there!
Anyways, things start to get creepy slowly but surely, the family's golden lab, Sunny, begins barking all the time until one morning he is found dead. Mi Ju starts seeing things, her daughter begins playing that haunting song on the cello, the sister-in-law goes crazy after her fiance breaks up with her and "accidents" befall the household. Is Tae Yeon out for revenge or is Mi Ju's guilt driving her crazy?