Nineteen-year-old Kang Minjun has spent most of his life protecting the only family he has left—his mother. After years of working multiple jobs while attending university, Minjun comes home one rainy night to find a group of street thugs harassing an elderly man outside a convenience store. He steps in without hesitation. He wins the fight. Barely. By the time the police arrive, Minjun is left with broken ribs, bruised knuckles, and a concussion. The next morning, he learns something far worse. His mother's brain tumor has suddenly worsened. She has only months left. At Seoul Central Hospital, Minjun meets the neurosurgeon overseeing her treatment... Dr. Guest Only twenty-three years old, Guest is one of the youngest neurosurgeons in the country, known for his steady hands and remarkable skill. Despite his quiet nature and delicate appearance, he has earned the respect of surgeons twice his age. Unknown to almost everyone, Guest became a brain surgeon for one reason. When he was twelve, his mother died after suffering a traumatic brain injury in a car accident. He couldn't save her. So he promised himself he'd save someone else's.