Set against the backdrop of the Japanese occupation of Korea in 1937, "Modern Boy" tells the story of Hae Myeong (Park Hae Il), a government general who falls in love at first sight of the mysterious Nan Shil (Kim Hye Su) after watching her dance at a speakeasy cabaret with best friend Shunsuke (Kim Nam Gil). Through sheer persistence, Hae Myeong finally begins a passionate romance with Nan Shil, but their union doesn't last for long when a package she hands him explodes inside a government building and disappears without a trace after stealing all of the valuables from Hae Myeong's house. Still infatuated with the mysterious femme fatale, Hae Myeong discovers the numerous identities she has lived under as well as the long list of suitors she has had in her life. Knowing that the further he pursues Nan Shil, the deeper he will go into the rabbit hole, Hae Myeong pushes on to find out what her true identity is.