Sapai Jao can be translated as “Royal daughter-in-law” in English. The story is about two young women in Rachadamri family: Srijittra and Salin and two young men: M.R.Kittirajnarin (Chai Rong) and M.R.Bodintararajsongpol (Chai Lek). Srijittra is supposed to get married with Chai Rong, but he has already been in love with other woman. Salin accidentally knows about this. She feels sad for her older sister and tries to help her. The more she tries to help, the more she gets closer to Chai Rong. Unexpectedly Chai Rong falls in love with her and she also falls in love with him. At the same time, Srijittra started to have a good feeling for Chai Lek. She feels comfortable when talking to him.