For most people, family is important. For Seo Do-wook, it’s everything…especially when it comes to his stepsister, Han Gayoung. After Gayoung’s mother passed away when the two were young, Do-wook made a promise to do everything in his power to keep his noona safe. But when their father marries again to a wicked woman determined to make their lives a living hell, it proves harder than he thought. Attempting to escape, the two move out on their own only to be presented with a new problem. As their once familial love begins to turn into tangible desire, will the two step-siblings be able to resist temptation? Or will they give in to themselves and take their relationship one step too far...?