After his mom left him with no reason, his staff didn't ever see him smile or laugh, they just saw his straight face. One of his best friend also known as his staff, Kim Taehyung really worried about him. He try his best to help him to be a cheerful man like before, but he also can't. One day, Taehyung younger sister just come back from overseas after her graduate, she want to search for a work, so Taehyung suggest her to work at the same company as him. Will she success to make his brother's best friend to be a cheerful like before?