Lee Gang, overseeing state affairs on behalf of the ailing king, cannot forget the Crown Princess who died unjustly and spends each day in torment. Left State Councillor Kim Han Chul, driven by boundless ambition, seeks to consolidate his power by marrying his daughter to the Crown Prince. Meanwhile, Dal, a peddler who has lost her memory, heads to Hanyang to save Lord Heo's daughter.
Dal uses her wits to rescue Lord Heo's daughter late at night. However, the household servants block her way. Gang and Prince Je Un arrive just in time, saving Dal and the young mistress. Out of gratitude, Dal promises to treat Gang to a bowl of rice soup. The next day, Dal is falsely accused and suddenly branded a thief; she eventually gets dragged away to face punishment.
After finding out U Hui is the Left State Councillor's daughter, Grand Prince Je Un decides to let her go. U Hui demands that Gang personally fetch her from Sinjusa Temple, so Gang heads to the temple. On the way, Gang meets Dal, who was also headed to Sinju Temple. Upon Gang's arrival, mysterious assassins storm into Sinjusa.
Gang and Dal get attacked by the ruffians that U Hui sent. Fortunately, Shin Won comes to their rescue right on time. Gang must save both the King and Je Un, and he needs to come up with a wise solution. Meanwhile, Dal is rewarded by Gang with silk clothes, which later gets her into trouble.
Dal and Gang wake up having swapped bodies and are both shocked. Gang tries every possible way to get into the palace, and eventually, with the help of the Queen Dowager, enters the Crown Prince's quarters disguised as a eunuch. They attempt to recreate the situation from before their bodies were swapped, but no matter how many times they try, they cannot return to their original state.
U Hui and Je Un witness Dal and Gang sleeping under one blanket. The rumour spreads, so Gang, who is in Dal's body, leaves the palace and stays in hiding for the time being. However, Gang is captured and is about to be punished. Right then, the Queen Dowager comes to the rescue. Meanwhile, the Left State Councillor finds out that Lord Heo helped Dal.
After being attacked by the Chief Court Lady, Gang believes it'd be best to avoid being with Dal to protect her. Gang keeps avoiding and hiding from Dal, which makes her frustrated. Gang figures out that the Left State Councillor still has the Jimjo Bird, so he decides to find a way into the Left State Councillor's estate. Meanwhile, Dal gets falsely accused by the Left State Councillor, and she is left to be flogged.
After the flogging incident, Gang takes Dal in as his concubine. Gang finds evidence that the Left State Councillor used the Chief Court Lady to take care of the Jimjo. Gang sets off to find the Jimjo himself, but the Jimjo behaves in an unforeseen manner, attacking everyone at the palace, including Dal.
Gang and Dal figure out that their bodies swap when their blood and water meet. Gang and Je Un find the connection between the Choraengi Mask and the former Chief Court Lady, and they search for the body in the cave where the Choraengi Mask disappeared into. Meanwhile, Dal gets accused of bringing Jimjo to the palace and gets interrogated.
Gang is shocked to find out that the King himself released the Left State Councillor from the Royal Investigation Office. He learns of the secret pact his father made after the Gyesa Year incident. Gang is left with no choice but to carry on with the Royal Wedding. Meanwhile, a fragment of Dal's memory returns.
Even after some of Dal's memory returns, she decides to return to the palace and stick by Gang's side instead of running away. After losing U Hui, Je Un begins acting strangely, looking like he's determined to get rid of the Left State Councillor. While trying to find the Left State Councillor's private army, Gang finds out who Dal really is.
The Left State Councillor apprehends Dal's parents and Hong Nan to have them executed. He demands Dal to expose her true identity to save them, and Dal reveals that she is the Deposed Crown Princess. She is imprisoned, but with U Hui's help, she escapes and heads to Mount Gamak to find proof to bring down the Left State Councillor.
Prince Je Un finds the hidden message in the military treatise that shares the location of the Left State Councillor's private army base. Je Un unites with Gang in Dal's body, and they meet Deok Chun, who tells them about the lady who holds the secret pact. Meanwhile, Dal secretly meets U Hui and shares her plan on the day of the Royal Wedding.
The Left State Councilor takes Dal hostage and storms into the palace with his private army. He threatens Gang to bring Queen Jangjeong. Gang has no time to hesitate as Dal is in danger. After the Left State Councilor's crimes are revealed, U Hui gets imprisoned, and when Un comes to rescue, she refuses to leave.
