For me, this is the touching story of the slow and difficult growth of the love between Joo Hong Bin (Lee Dong Wook) and Son Se Dong (Shin Se Kyung), And the love between Joo Hong Bin and Chang (Jung Yoo Geun), his child, whose existence he has just learned about.
There are flaws, or faults, in the plot, but the main story-lines and the acting compensate for that. The acting, and charm, of the son, (Jung Yoo Geun) is amazing. Particularly in the scenes where he is expressing joy and a sense of freedom.
There is a side to the story that is almost unbearably sad, but the characters, and we, the audience, cope with it.
This is one of thee most addictive series I have watched. It led to too many late nights.