Standard someone gets whacked: who did it and why?
Standard rich family and internal mess.
To differentiate itself from being a boring rehash of similar situations, the series banked on weird things. Thus, the rich family is made mostly of incompetent (how could it have made it big?). The homes are huge and uncomfortable. The people have weird relationships: wife can't like hubby, who anyway sleeps around elsewhere, and is totally unaware of the wife [why did he marry her?], son fools around with maids, other guy is a control freak, matriarch likes birds, the nun is an ex-gisaeng, who in the end leaves her vocation, head of maids is another "masterpiece", etc. This mess remains a mess throughout the whole series.
In the end you get to see why the guy got wacked, how, and by whom, and then you ask yourself: so what?