It tells the story of a woman who hired a mercenary to marry her for a year. She is the only daughter of a large construction company, who wants to free herself from her grandfather's control and dedicate herself to painting. He is a former soldier with an unpredictable personality, who works for a private military company. They begin a fake marriage for 20 billion won, but soon find themselves involved in several hilarious and dangerous situations. Will the two be able to keep the contract until the end, or will they truly fall in love?