Taek-seon, a translator drained of energy, motivation, and any trace of romance, is going through a lifeless routine. After a disastrous blind date with Su-pil, a socially awkward researcher who proposes marriage on their first meeting, Taek-seon's world suddenly turns rosy the very next day. She finds herself smiling for no reason, drawn to flashy dresses she would have never looked at before, and even the daily texts from her old classmate Yeon-woo feel endearing. But when she learns she has been infected by a fatal virus and meets Lee Gyun, the only researcher capable of developing a cure, Taek-seon realizes all these changes are symptoms of the virus.