Yoona has a son named Yoogeun. His real dad doesn't know that he got Yoona pregnant so she took care of Yoogeun by herself. Yoogeun turned 7 knowing that the guy on a photo that Yoona always show to him is his father. Yoogeun forced his mom that he really wants to meet his dad so badly so that his family will be complete and his friends won't anymore.

                When fate gives Yoona a chance to meet the guy who is named Minho, she offers him a contract if he can be his husband and the father of his son for 3 months. At first, Minho doesn't want to accept the offer but when he saw how Yoogeun cute is and a very good boy, he signed the contract with Yoona. He starts living with them as a fake husband and dad. 

Im Yoona - She is a rich girl and a single mom. Though she has everything she needs, she can't find a way to grant Yoogeun's wish and that is to meet his father. At first, it really bothers her when Minho is only nice to Yoogeun and not to her. But as thye've been together a little longer, they've became sweet with each other and Minho treats her so well like she is his wife. Later on, Yoona starts to fall for him but she can't admit it to herself.

Choi Minho - he will act as a husband and a father. Though he is rude to Yoona when they are just starting to pretend. He starts to realize that he should do his best in portraying his role and be a good guy to Yoona.  When his relationship with Yoona starts to develop even better, he begins to love Yoogeun and Yoona.

Im Yoogeun - Yoona's son who always wished to meet his dad and have a real family. Yoona made a good job of taking care Yoogeun by herself because he turns out to be friendly and protective over her mom. He always loved his father though he hasn't seen him for 7 years, only in a picture.