In the second episode of Moon River, we are transported back five years through a haunting flashback. King Lee Hui sends a chilling message to the crown princess, urging her to sacrifice herself for the crown prince's sake. Her obedience to this demand sends her plunging into the icy waters of a lake. A court lady, none other than her Aunt Hong-nan, gives chase, but to no avail. The princess is found near a magical tree adorned with flowers, lying unconscious on the ground.
Wolha appears, revealing that the red mark on the princess's hand is a sign of a sealed red thread—a curse that has erased her memories. He warns Aunt Hong-nan to keep the princess's past a secret, lest she regain her memories. As the princess awakens, she is told by Aunt Hong-nan that her name is Dal-i and that she is her aunt.
Meanwhile, Yi Kang and Je-woon delve into their investigation of Kim Han-chul's involvement in the Gyesa Year incident, during which the previous king and his second-born son fell ill while engaging in a wooden sword fight. They have been unable to find any evidence linking to Yi Kang's mother's murder, so they turn their attention to the poisons that can be administered through a wooden splinter with no other symptoms. The doctors they question all refer to the poison of a Zhen bird, a mythical creature from Qing history.
Je-woon finds an old man who once possessed a Zhen bird and sold it, and they realize that Han-chul was traveling at the same time as the bird was sold—he could be the buyer. As Yi Kang leaves, Dal-i falls from the roof right into his arms, surprising him so much that he drops her in shock. But then he hugs her, and she is forced to push him away. After dressing in her own clothes again, Dal-i tells the two cousins that she is a porter from Boryeong.
Suddenly, Dal-i remembers her duty to help Lady Heo and rushes out, leaving her things behind. In her bag, the brothers find her notes for Lady Heo and realize she is in danger. Lady Heo sneaks out of her house and Dal-i hides her in her porter's box. Unfortunately, they are caught and about to be dragged home when Je-woon arrives in the nick of time, allowing them to run away. However, Yi Kang stops them and allows the men to take Lady Heo away. Dal-i argues with Yi Kang and, in the process, utters something that the crown princess had told Yi Kang. He asks her if she knows what happens when you catch a falling petal, testing if she says what the crown princess used to say.
She remained silent, and Yi Kang made an offer to secure her response. If he could resolve the matter with Lady Heo, she was bound to give him her answer. Yi Kang set his course towards the Kim household, where Lady Heo resided. Overhearing her, he heard her pleading for her life, and witnessed her tying up her father-in-law, Kim Ji-pyeong, warning him against laying a finger on the girl.
Meanwhile, Dal-i stirred up the other villagers and led them all to Kim's house to protest the forced suicide. By the time she arrived, Yi Kang had already sorted things out. However, royal guards were brought into the house by someone else, and Yi Kang played the role of a royal inspector, telling them to arrest Kim Ji-pyeong. He then turned to Dal-i for her answer about the falling petal, but she didn't give him the answer he wanted. Yi Kang looked heartbroken, and Dal-i suggested buying him some food to comfort him.
Back in the royal palace, Han-chul was displeased by Yi Kang's act of kindness. He ordered his daughter Woo-hee to come to the palace. But Woo-hee used a gun to shoot bullets into her father's message. A flashback revealed that a year ago, Je-woon had made a drawing of her—it turned out that they were in love.
While walking with Dal-i, her parents suddenly appeared. She hurriedly told Yi Kang to meet her the next day and rushed off with her parents. When they were in a safe place, Dal-i revealed that she knew her father was a eunuch in the palace and her mother the head court lady. They had an affair and fled the palace. Dal-i said she had known this for a long time.
As they slept, Dal-i snuck out. She arranged for Lady Heo a new home. On her way back, she met Je-woon, who seemed impressed by how many merchants she knew across the country. He told her to meet him after her lunch with the "inspector." Later, Je-woon overheard Kim Ji-pyeong's servant vowing revenge on Dal-i.
Meanwhile, Yi Kang waited for Dal-i at a tavern with Shin-won and his eunuch Se-dol. Dal-i's parents walked by and Se-dol almost recognized her father. As Dal-i headed to the tavern, Kim Ji-pyeong's servant framed her for stealing. The nearby guards arrested her and took her to Dobong, a headquarters for travelling merchants. There, her protests fell on deaf ears, and she was sentenced to beatings as well as a leg amputation. Fortunately, Yi Kang stormed into the place just in time and saved Dal-i from certain doom.
