Injo hastens the second Manchu invasion of Joseon, with his act of defiance by pouring the blood he’s supposed to drink, at a ceremony where he was supposed to pledge his allegiance to the Manchu kingdom. His paranoia with Jung-myeong brainwashing So-hyeon clouded his judgement, and strengthens his fear and desperation for holding the absolute power and authority as King. So-hyeon was made to call him King, instead of Honorable Father, and So-hyeon crumbles in dispair at the change of Injo’s attitude to him.
While Joseon is still in the midst of recovering from the shock of Injo’s actions, the Manchu army wastes no time in invading Joseon for the second time. Because previously Injo always retreated to Kanghwa Island, the Manchurians have learnt to cut off the escape route to there. Jung-myeong foresees the possibility of Manchurians doing that, and tries to advise Injo for retreating to somewhere else. Despite her foresight, the combination of treacherous minister in the form of Kim Ja-jeom and Kang Joo-seon allowed for a full force invasion, by preventing an relaying of messages to the palace that the Manchurian army has already breached Joseon’s defence and is right at Joseon’s doorstep.
Hence, the famous “kneel thrice and kowtow nine times” event happened, where Injo was stripped of his King garbs and kowtowed nine times to Hung Taiji. It is an ultimate insult to the Joseon kingdom, as they’re bound eternally to Manchu as a vassal state instead of an independent country. So-hyeon and his brother Bong-rim (future King Hyojong), as well as their family members, head to mainland China as hostages for a good eight years, to ensure that Joseon will not be invaded again.
Kim and Kang wanted to have So-hyeon killed instead, because they view him as an obstruction to their success, be it controlling the entire government, or exploiting the commoners and earning more money. These two men are willing to sacrifice their country for their own selfish needs, and it’s especially angry to watch them getting their ways, while our good guys were trying to protect their country and the people from becoming slaves to the bigger country (many Joseon people were forcefully taken away to China, and never get to return to Joseon). History keeps repeating itself because people like Kim and Kang always exist, as we can see in modern Korean history, when Korea become occupied by Japan.