I'm pretty sure "The Heirs" is trying to make some sort of statement about traditional masculine gender roles in a courtship context, but I'll be darned if I have any idea what. The imagery this time around is too inescapable. This episode Eun-Sang receives come-ons, not just from leading men Kim Tan and Yeong-Do, but extras. And there's a strong frustration underscoring her reactions to these events that emphasizes the importance of diplomacy in her responses- she'll only go as far as she can without risking damage to her long-term prospects.
What makes this especially nuanced and difficult is that it's explicitly confirmed this episode that she does like Kim Tan. But this revelation doesn't mark the jubilation that Kim Tan would be hoping for, because in the same scene there's this emotional bluntness in Eun-Sang's dialogue that really hits hard. Kim Tan's character as a whole receives a lot of punishment this episode, and it feels fairly well-deserved.
Contrast his big bro Kim Won- who shows remarkable diplomacy and consideration for other characters' feelings, at least to the extent he's able. He has this great scene with Rachel Yoo that really shows off how she is a woman that can be negotiated with pretty easily. The main cause for her antipathy with Eun-Sang can be laid directly at Kim Tan's feet- whether Kim Tan will ever figure this out remains unknown, but it's certainly easy to see why he idolizes a big brother who clearly doesn't even like him.
Contrast the bad influence of his mother Gi-Ae, who actually gets to do something this episode. Something exceptionally bizarre and short-sighted, and I like how every character who knows who Gi-Ae is immediately calls her out on how insane and risky this is. Kim Nam-Yoon doesn't show up this episode, but the preview makes him look panicked. Really, it was only inevitable that his elaborate games of fourth dimensional chess would backfire somehow.
One last plot point I liked- Yeong-Do playing detective. In the first place he's good at it, and this is a very useful skill to have in an environment where nearly every character is hiding some sort of essential secret. But it also brings rise to the question of what he's going to do with this information. Yeong-Do doesn't seem particularly interested in blackmail- maybe just the feeling of power it gives him? In any case, the action this episode is pretty riveting and exemplifies a lot of what this drama is able to do well.