Based on the biblical story of Adam and Eve's first two sons, Cain and Abel is about Cain's jealousy towards his brother Abel. Lee Cho In is a very gifted doctor who has everything that he wants whereas his older brother, Sun Woo, is jealous of all the attention that Cho In receives. Sun Woo blames his brother for taking everything good in his life away from him. Sun Woo blames Cho In for getting their father's love, getting more recognition as a doctor, and for stealing the woman he loves.