Kim Jongin and Byun Baekhyun, a young married couple that have 3 sons, the oldest Kim Jongdae and the twin Kim Minseok & Kim Kyungsoo.

Unfortunatelly, all the married couple problems they have to face when they were still so young, brought them to the end of the line. they finally agree to divorced when Jongdae still 5 years old and the twin still 2 years old... They decided that Jongdae and The youngest, Kyungsoo will live with Baekhyun at  their apartment, meanwhile Minseok will live with Jongin and move out from there.

Jongin move with little Minseok to the other room on the other floor but still in the same apartment building, since Jongdae crying hard and beg that he still want to meet His dad and his little brother often, so Jongin agreeing to still live on the same apartment building. Jongin move to the 11th floor meanwhile Baekhyun at the 5th floor.

Jongdae is a "wise" child so he decided that if today he lived with his umma, tomorrow he will slept on his appa's apartment, so he won't miss his beloved appa and umma.
Every single day, Jongdae always hope to god that his Appa and Umma will back together.. But unfortunatelly, what he hoped never come to him..

2 years after the divorced, Jongdae continue his live as a "wise child" but thats started to change when his umma introduce a man named Park Chanyeol to him, and he knows that this Chanyeol guy is his mother's boyfriend, and he didn't like it. He don't want to have any other dad except his Jongin Appa. After that, Jongdae lived much more often with his dad.

Jongdae never once like Chanyeol, everytime he come to his mom house, Jongdae will throw a tantrum to Chanyeol. Meanwhile, his dongsaeng, Kyungsoo was already close with Chanyeol (even Minseok who's barely know Chanyeol was did good with Chanyeol like his twin brother did). One day, Chanyeol and Baekhyun tell Jongdae that one day, maybe in a few months or a year or later, they will get married. After that, Jongdae crying 'cause he knew that his parents never gonna be together anymore, because his mother already have someone else other than his appa.. And with that, Jongdae decided that he want to move to his Appa's apartment.

Jongdae refuse to answer when Jongin asked why he suddenly want to live with him so he asked Baekhyun and Baekhyun told him about Chanyeol and how Jongdae doesn't like Chanyeol. Baekhyun also asked Jongin if he can bring Jongdae and Minseok tomorrow for go to ammusement park with him, Kyungsoo and also Chanyeol, and Jongin said yes but Jongdae refuse to go if Chanyeol was there to go with them.

After knew why Jongdae "run away" from Baekhyun, he can't deny that he feels insecure now, because actually he also already dating someone else.. he already dated Oh Sehun for the past 3 months.. He also already introduce Sehun to Minseok (but still introduce him as his very close friend) and Minseok have a really good term with Sehun (Jongin always think that Sehun will be a good mom for minseok and he know he's true even Sehun himself doubt it).  Sometimes when Jongin is busy, Sehun will volunteer to babysit Minseok and Jongin can't be happier that his lover loved his son like his own child. Even Jongin already intoduce Sehun to his youngest son, Kyungsoo. But now he don't know how to introduce Sehun to Jongdae.... Jongin doesn't want Jongdae hate Sehun like he did to Chanyeol, but same as Baekhyun who planned to marrying Chanyeol, he's also planning on marrying Sehun. But before that, he must introduced his lover to his oldest son. What will happen to Sehun and Jongdae when finally Jongin introduce them to each other?