The romance story of an excellent neurosurgeon and a determined endocrinologist. Han Seung-joo (Ji Hyun-woo) used to be a warm and an understanding person, but after the death of a close friend, he became a hot-headed person and merciless towards others. After listening to the rumors of how Seung-joo has turned into a completely different person, Joo In-ah (Lee Si-young) can't help but feel intrigued towards him, believing that all of that temper is because of hormones. She is determined to make him as her patient, and run a blood test on him to check on his hormone levels. From then, their rivalry begins.