It looks almost as a oath, Mimi (Rene Liu) would receive a birthday greeting message from Nam (Louis Koo) even after Nam got married four years ago .…

Nam and Mimi once were lovers when they were University students. Because Mimi didn’t want to lose Nam, she therefore suggested being best friends and believed it was the best way to keep the romantic relationship. Eventually, they separated even they still love each other.

Years past, they met on the street again… Nam had changed many girlfriends these years. The reason is his heart was still having Mimi, therefore he couldn’t have long relationship with any woman. They knew they still love each other, but not dared to tell. And they kept the so called "soul mate" relationship.

Nam’s girlfriend Yoyo left him when she realized Mimi was the one still in his heart. During that time, Mimi went to Japan for further studying. Nam visited her, because of some misunderstanding he gave up to propose to her and back to Hong Kong. Later. Mimi was told that Nam was married with Yoyo. Mimi was not too sad because she thought that was the way they were. As long as she could receive the stable birthday greeting from Nam, or the SMS "Happy Birthday" every year, love between them still existed.

In fact, Nam already had passed away because of the lung cancer… In order not to upset Mimi, Nam made up the story as his marriage to go away and asked his sister to do his favor as such keep on sending the birthday greeting to Mimi. His last wish is to make Mimi to carry on her life even without him around…to keep their true love last forever.