Twenty-five years ago, high school student Nam-mi (played by Shin Eun-kyung) moved from Jeolla Province to Seoul with her family. Nam-mi enrolled at Jindeok Girls' High School, and because she was shy to speak due to her strong dialect, she was fortunate to receive protection from her class elder sister, Ha Cheon-hwa (played by Kang So-ra). She met five girls who surrounded Ha Cheon-hwa: Kim Mi-kyung, who was obsessed with double eyelids; Hwang Jin-hee, who had a foul mouth; Seo Geum-ok, who dreamed of becoming a writer; Yoo Bok-hee, who aspired to be Miss Korea; and the silent and proud beauty, Jeong Soo-ji. After a confrontation with a group of troublemaking girls, Cheon-hwa, Nam-mi, and the other seven formed a group called 'Sunny'. Years later, Nam-mi, now a housewife, unexpectedly reunites with Cheon-hwa, who is hospitalized with a terminal illness, while visiting her mother. Cheon-hwa hopes to see the other Sunny members again in the final two months of her life. Nam-mi reaches out to Kim Mi-kyung, and the two hire a private investigator to find their old friends, awakening memories of their youth behind each familiar name.