Ok Taek-Sun works as a translator. She doesn't have energy or motivation due to a loss of her love cells. After a chaotic blind date with Nam Soo-Pil, her personality changes completely to being bright, happy, and romantic. She laughs for no reason, and she is drawn to a colorful one-piece dress that she had no interest in before. Even a group text message for business from her alumnus Kim Yeon-Woo, that rings every day, brings her joy. She then learns that she is infected with the Toxovirus that has a fatality rate of 100%. The virus causes her to fall in love for no reason. Her sudden changes in mood are due to the virus. She has an encounter with virus expert Lee Kyun, who is the only person that can create a cure.
