In Hong Kong, Dr. Gao Jing is introduced to the brother of her best girlfriend Chen Xiao Kai, the photographer and diver Dave Chen Guo Dong. They fall in love with each other and Guo Dong invites Gao Jing to travel to Taiwan to visit an ancient submarine city, where he intends to propose her. During the dive, Guo Dong vanishes. Gao Jing cannot recall what happened underwater. She decides to investigate.