Choo Yeong Woo Sets Out on a Journey Alone, Leaving Lim Ji Yeon Behind in "The Tale of Lady Ok" Episode 4

Sung Yoon Geum learned about Ok Tae Young's real identity as Gudeok and in return, he revealed his secret as well to her. He's a man that cannot embrace a woman and even with this he proposes marriage to Tae Young and promised to protect each other's secrets. With that, their marriage proceeded and there, Cheon Seung Hwi (the story teller) found out that Gudeok's groom shares the same identical face as him. This instantly became the saving grace of Yoon Geum later in the show though.

One of the villains, Lee Chung Il, commenced a mining with workers composed of young slaves to get him gold in the mountains. Afraid that he might get caught doing this illegal mining, he had to stop the magistrate from doing raid in the mountains by discovering and revealing about the Devoted Hearts Organization. This secret organization helps those children who are considered an outcast during that period of time. It turned out that this secret organization's leader and founder was none other than Sung Yoon Geum. His mission was to rescue and protect those people who are like him (yes, in a much understandable word, he's homosexual). During this period of time that they're living in, homosexuals aren't accepted even if they're born nobles which is why Yoon Geum trained the people he rescued some self defense to fight for themselves against oppressors. However, Lee Chung Il identified them as rebels quickly and caused turmoil in their country which led to the magistrate losing his position. Something that made Lee Chung Il victorious. 

Every member of this secret group has a Chinese character of heart stamped on their shoulder, therefore Yoon Geum has this mark. The only reason he survived the search was because Seung Hwi helped him by switching with him before showing his shoulder to the military. And once Yoon Geum survived, he went out on a journey alone, living his father and Gudeok behind. 

I honestly feel bad for Gudeok here, he has no one to turn to again. Magistrate is out of office and her husband has to hide from their country. I guess, only this way, she'll be able to reunite with her first love, Cheon Seung Hwi and be together this time. Seeing the preview for the next episode, it seemed like Gudeok will once again have to return as a slave as she goes on a journey with the story teller until her husband return to their land.