Mi-so, a 12 years old girl who transferred from Seoul to Jeju island, meets Ha-eun. They promise never to seperate. At the age of 18, Ha-eun's boyfriend, Jin-woo breaks two girls's friendship. Few years later, they come apart as their lives go seperate ways. Now they are 27, and they finally meet again. They've missed each other. After 15 years, will they truly understand each other?