The story begins with Shim Changmin standing in front of the funeral pyre of his wife Victoria. Through a series of flashbacks Changmin recall their marriage, their honeymoon, Victoria's pregnancy with their son and the child's eventual birth. It is revealed that Victoria was aware of complications in her pregnancy, during which only mother or child could be saved, but decided not to tell Changmin as she knew how much he wanted a child. During her pregnancy, Victoria, who also loved the baby more than her own life, writes eight letters to her son(one for each of his first eight birthdays) and gives them to Changmin's mother  Jaejoong. Before dying, Victoria asks Changmin to promise her to name their son as Minhyun.

Eight years go by and  Changmin is now a single parent living with his son Minhyun and his parents Shim Yunho and Shim Jaejoong. His mother worries that Changmin will end being lonely and that Minhyun keep missing out on a motherly figure in his life, but Changmin brushes it off saying that having him and his parents is enough for his son.

On his eighth birthday, Minhyun reads the last and most important letter that his mother left him; it tells the story of Changmin, Victoria and Kyuhyun.

A flashback begins from St. Xavier's College, where Shim Changmin and his best friend, Cho Kyuhyun who were most popular students of their times. The two were close friends but deny any romantic feelings for each other.

The college principal, Zhoumi states that his daughter Victoria is coming to St. Xavier's from London to finish her degree, and asks Kyuhyun to be her guide and friend. Victoria quickly becomes friends with Kyuhyun and Changmin, and Changmin constantly flirts with Victoria, trying to win her over.

As time goes by, Kyuhyun realises that he is in love with Changmin, and is encouraged by his motherly guardian Leeteuk to confess Changmin about his love for other. Before he is able to declare his feelings for him, Changmin instead tells Kyuhyun that he is in love with Victoria. Devastated, Kyuhyun decides to leave college and shares a tearful goodbye with Changmin. Although she is in love with Changmin, Victoria realises that she came between him and Kyuhyun and their true friendship.

Back in the present, Victoria explains in her letter to her son Minhyun that Changmin always said that love is friendship, and without friendship there can be no love. Changmin is a single parent and lacks a friend in his life, so Victoria gives her son the mission to reunite Changmin with Kyuhyun and bringing back Changmin's lost love and his best friend.

The next day, Changmin, Minhyun and his eomma Jaejoong head to China where they meet Zhoumi for Victoria's death anniversary. There Minhyun shows them, except for Changmin , his mother's letters. They tried to find Kyuhyun but Kyuhyun already changed his house. They pursued Leeteuk to reveal Kyuhyun's whereabouts. Innocent Minhyun was able to convince Leeteuk and he finally gave up informations about Kyuhyun.

Kyuhyun is no longer same as he was in college, he has become a beautiful man and is now engaged to Choi Siwon, an CEO living in London. However, he explains to his mother Heechul that he does not really love Siwon and is marrying him as a compromise as he feels he can never love again after losing Changmin. Siwon also suspects that Kyuhyun does not really love him.

Cho Hangeng and Cho Heechul who witnessed their only child's heart breaking moments and lost love was not able to heal Kyuhyun completly. Eventhough Kyuhyun was smiling outside they both know their son was just wearing a mask. Kyuhyun already knew that stuborn Changmin will come in search for him so he convinced his parents to move house and keep him away from Changmin and Victoria's life. 

Determined to reunite his father and his best friend, Kyuhyun, Minhyun and his grandmother search for Kyuhyun and soon learn that he is going to work at a summer camp in Busan. Eventhough Leeteuk mentioned that now Kyuhyun is engaged and going to get married soon, does not have effect on Minhyun's decision to reunite the two best friends.

Changmin told his son that he was not allowed to attend the summer camp and heads to a business conference, only to find out that his eomma and son went without his permission, having left a letter for him.

They travel to the camp, with a plan to later lure Changmin to come as well, and meet each other.

Minhyun met Kyuhyun who was distributing balloons for the kids. When Minhyun approached Kyuhyun, Kyuhyun felt sorry for the younger one since no balloon is left to give him. Kyuhyun felt strange as if Minhyun was his own child. They were having smiliarities. Somehow child's bambi eyes attracted him alot. Those eyes also reminded him someone who he always wanted to forget.

Kyuhyun: I am soo sorry. I will try to get you something else. What about a candy?

Minhyun: It's okay. Appa told Minhyunie not to eat candies alot.

Kyuhyun: Minhyun-ah your name is so sweet. My name is Kyuhyun.

Minhyun: Why is your name Kyuhyun?

Kyuhyun: M-hm may be my parents like that name. What about your name Minhyun-ah?

Minhyun: May be my parents like you.

Kyuhyun: Huh?!

Kyuhyun felt strange but comfortable when he was near Minhyun. They become closer day by day.

Changmin appeared in a kids live show which Minhyun always watched at home, to send a video message to Minhyun stating that he missed his son alot and also asked Minhyun to come back home soon from Summer Camp.

While watching television, Kyuhyun realizes that he has met Changmin's son, and that Victoria is dead. Few hours before he found Minhyun praying to God to keep his appa safe and happy. Curious Kyuhyun asked why all prayers only for his appa and not for eomma. Then Minhyun revealed that his eomma is with God and she can ask herself to God anything she wants.

Changmin soon arrives at Camp Sunshine, after his son fakes a fever, where he and Kyuhyun are surprised and delighted to see each other again, sharing a sweet reunion.

Changmin: Kyuhyun...

Kyuhyun: Hey Changmin. How's your life?

Changmin: As you can see.

Kyuhyun: You will never change. I am sorry about Victoria. I didn't know.

Changmin: Yes. How would you know? You dissappeared.

Kyuhyun: My parents and me moved to a new neighbourhood.

Changmin: I know. And does that mean that you moved out from our friendship too?

Kyuhyun: No. Just this and that.

Changmin: When I needed my bestfriend most, you were never there.

Kyuhyun: I apologize for everything.

Changmin: Leave it. Hey look at the sky. It's a tooth fairy.

Kyuhyun: You still believe in this?

Changmin: No. What about you?

Kyuhyun: No

Both wished something in heart turning their heads on opposite sides. And started to laugh like idiots.

Changmin: Kyu, what you wished!

Kyuhyun: Kekeke Goodnight Chwang.

Changmin: Goodnight Kyu.

Throughout the days spent at the camp, Changmin and Kyuhyun felt themselves falling in love with each other. Just as they were about to share a heated moment, Kyuhyun thought about his engagement and felt guilty. He runs away from Changmin in tears. He stared at his engagement ring. Two arms wrapped him from behind. He thought it was Changmin but found his fiancee Choi Siwon as the one who hugged him.

Kyuhyun hold in his tears, after when Siwon arrives and introduce himself to Changmin that he is Kyuhyun's fiancee. Changmin is left heartbroken but congratulates Kyuhyun. Kyuhyun takes this as Changmin rejecting him again, so he leaves the summer camp and decides to get married to Siwon as soon as possible.

After seeing Victoria in a dream were she motivates Changmin to get his love back, Changmin and his family go to Kyuhyun's wedding, where Changmin silently confesses to Kyuhyun that he loves him, and watches in tears as Kyuhyun is brought forth for the wedding altar.

Realising Changmin's love, Kyuhyun remains hesitant to go on with the marriage, and stands weeping infront of Changmin looking into each others eyes.

Siwon notices the tears in Kyuhyun's eyes and realises that he has always been in love with Changmin. He releases Kyuhyun from the engagement and convince him to marry Changmin.

Changmin and Kyuhyun had an emotional hug and as the two marry, little Minhyun sees a vision of Victoria, who is smiling and giving him the thumbs up. Kyuhyun and Changmin get married happily. Their small family is complete with both of them and their favourite Minhyunie.

 
Changmin: Kyuhyunie Do you remember something?

Kyuhyun: What Chwang?

Changmin: I used to tell something about love and friendship.

Kyuhyun: I remember. You said that for you Love is Friendship.

Changmin: For me i always felt that without friendship there won't be true love .

Kyuhyun: I can understand Chwang that you love Victoria alot. And you might be missing her.

Changmin: I miss her as a friend. She was my friend, lover and wife.

Kyuhyun: I know.

Changmin: But my bestfriend was always you. I missed you the most durning these years. Even when I was with Victoria, even after she died I missed you more than her. Because I loved you more than anyone else.

Kyuhyun: Chwang... I...

Changmin: Let me speak Kyuhyunie. I love you. In past, In present and In future too.

Kyuhyun: You don't know how long I have waited for hearing these words from you.

Changmin: I was a stupid who never realized my love for you at that time. But not anymore.

Changmin pulled Kyuhyun into a heated kiss. Minhyun watched his parents proudly. Suddenly Minhyun felt possessive. He should save his Kyuhyunie eomma from his erted appa. Minhyun entered into balcony and seperated newly weds. Changmin got annoyed  due to sudden change of romantic atmosphere.

Changmin: Minhyunie go and sleep with jae harmonie.

Minhyun: Shireo. I want to sleep with appa and eomma today.

Kyuhyun: Let him sleep here Chwangie.

Changmin: Kyu are you out of your mind? It's our first night.

Kyuhyun: So what? Our Minhyunie must be missing his parents. Kajja let's sleep Minhyunie.

Changmin: Sometimes I really wonder whether Minhyun is your own son Kyuhyunie. He is jealous and possessive just like you. He even looks like you.

Kyuhyun: Well Chwangie I also thought that he had more qualities of both of us. Evil, Lovely, Jealous, Possessive and Genious too. When I saw him first at Summer Camp. I felt like meeting mini Kyuhyun. And his eyes just like yours.

Minhyun: I am born to be your son Eomma.

Changmin: You are right Minhyunie. Okay you can sleep only today. Kajja, Kyuhyuine be in the middle of both of us on the bed.

Minhyun: I want to sleep in middle between appa and eomma.

"God! I should take Kyuhyunie to Honeymoon soon. Else Kyuhyun gonna remain as a forever. I wish for the first time that Our Minhyunie wasn't this evil to destory his own parents first night." Changmin thought in mind.

Changmin watched two beautiful persons smiling and hugging each other on his bed. He joined them without a second thought in their warm hug. This is the moment when his love is complete and this is the moment when his life is complete. Soon the small family of three dissolved into dream land of their own. Yunho and Jaejoong smiled happily witnessing everything through window.

IN YOUR HEART YOU WILL FEEL SOMETHING TO THAT ONE PERSON ONLY, WHO YOU TRUELY LOVE BEYOND ANY CONDITION.