Siwan, Eunsoo, and Chanhyuk are close friends who have spent 6 years in medical school, 1 year as interns, and 7 years together. They are accepted together as surgical residents and begin their lives as doctors with hopeful hearts. Eunsoo, who aspires to be a "Great Surgeon," tries harder not to be discriminated against for being a woman. However, the meticulous perfectionist chief resident Lee Seung-hyun treats her particularly harshly, and amidst all this, Eunsoo and Siwan slowly develop their friendship into love. As stress from residency life builds up, Eunsoo becomes increasingly irritable, and consequently, Siwan gradually finds himself drawn to Seung-hyun, who possesses more feminine charm than Eunsoo. One day, Eunsoo collapses in the operating room and discovers she has stomach cancer...