Man-sik’s younger brother Hyung-sik works with the coast guard. While on patrol, he rescues Hi-mi, who had fallen off a yacht. The beautiful and spoiled vacationer from Seoul is instantly drawn to her rescuer and launches a bold campaign to win his heart. Hyung-sik finds himself growing attracted to her little by little. 

Marine geologist Kim Hwi discovers the Korean East Sea is showing signs of activity similar to that of the Indian Ocean at the time of the tsunami and heads down to Haeundae to warn the authorities. He runs into his ex-wife who is also in Haeundae to oversee an international event. With her is their 7-year-old daughter whom he has never met. The fact that his daughter doesn’t know who he is gives rise to complex emotions in Hwi. 

In the meantime, a mega-tsunami is created as Hwi foretold and is headed straight for Haeundae, to the oblivious vacationers enjoying a peaceful, hot summer day.

A popular vacation spot on the south coast of Korea, Haeundae draws visitors from all over the country. During its peak season, one can find more than a million vacationers packed onto its narrow one-mile strip of sand. HAEUNDAE treads away from the Hollywood template for natural disaster movies. Rather than focusing on one hero that foretells the disaster and saves the day, it tells the story of different characters caught up in the drama that catches momentum with the arrival of the giant wave.

Rather than on tsunami itself, the film focuses on the touching drama surrounding the main characters who are connected by interwoven relationships – Man-sik, who prepares to propose to his long time girlfriend; Yeon-hee, whose chance to respond is interrupted by the unexpected disaster; Hwi, who meets his 7-year-old daughter for the first time but is unable to tell her that he is her father; Yoo-jin, who learns about the importance of family the hard way; Hyung-sik, who risks his life to save the one person he loves; and Hi-mi, who despite the disapproval of her friends, falls in love with Hyung-sik.