One day, Kim Da Hyun, a kind elementary school teacher, helps an old man get to the hospital, saving his life. Unknown to her, he's the owner of a large company and moved by her compassion, he names her his heir on the condition she marries his grandson, Lee Jae In.
Upon learning of this, Lee Jae In, a handsome and arrogant business man, seeks her to resolve the matter. Neither of them is happy with the extravagant conditions, as Jae In refuses to see his family's legacy go to an undeserving stranger and Da Hyun is uninterested in inheriting a company at all, plus neither can stand each other and deem marriage impossible.
As such, they manage to have the grandfather alter the conditions: if they manage to date for a full six months, then Lee Jae In will be able to inherit. But even six months seem unlikely, when they are two contrasting people that lead such different lives.