Seo Eun-il has had a one-sided crush on his childhood friend Nam Jeheon, now the CEO of IDBIO, for nearly a decade. As Jeheon's personal secretary, Eun-il spends plenty of time with him but struggles with his unspoken feelings. When Jeheon chooses to spend his birthday with someone else, Eun-il is left with an uneaten cake and unexpectedly encounters Jeheon's twin brother, Nam Pilwoo, who has just returned from the United States.

With secrets and long-held feelings bubbling beneath the surface, Pilwoo seizes the moment to seduce Eun-il, sparking conflict in the heart of Eun-il. As old memories resurface and hidden desires collide, Eun-il finds himself at the center of a tumultuous love triangle. In this battle of hearts, may the best brother win…