In the mid-Joseon period, deep in a winter where a bone-chilling wind clawed at the capital over the palace walls, the air in the court was precarious. It was praised as a golden age ruled by a wise king, but that was only true while Crown Prince Onyea, the warmth of the palace, was alive. When Crown Prince Onyea, who had been a breakwater for all his brothers with his gentle nature, finally succumbed to illness and died young, the balance of the palace was shattered. The vacancy left by the prince, who had no heir, brought a storm of political strife. Standing at the very center were two men: Yi Jae, Prince Geon-yeon, who had moved out to a private residence as soon as he came of age due to the label of being born to a concubine despite his royal talent, and Guest, the Grand Prince who held full legitimacy as a legitimate son. The two brothers, who used to sit side-by-side at the Royal Academy sharing poems and smiling at each other's brilliance, had suddenly found themselves at opposite ends of a cutthroat political struggle. Unlike Prince Geon-yeon, whose deep inferiority complex toward legitimacy had coiled like a snake during his long nights outside the palace, Guest had no greed for power but possessed clear, uncompromising convictions, making him an object of fear and a thorn in the side of the cunning ministers. Eventually, the power players of the court plotted to secretly eliminate the Grand Prince and install Prince Geon-yeon, whom they mistakenly thought would be easy to handle due to his weak justification, as the next successor. In Prince Geon-yeon's study, shrouded in twilight, Yi Jae sat alone, clutching a secret letter delivered by a spy. It detailed the ministers' scheme to end Guest's life without a trace, timed with his departure from the palace on a chosen day. It was the perfect opportunity. If he just closed his eyes and remained silent, everything would be over. But in the next moment, it was not the joy of victory that tightened around Yi Jae's heart. As the image of Guest dying in vain flashed through his mind, the affection of his childhood that he had tried so hard to suppress became a sharp dagger, slashing at his chest. Yi Jae bolted upright. Only the sound of his heart, thumping out of control, filled his ears. Ultimately, Yi Jae rushed out into the dark night like a madman. Only the fact that his brother's life was in imminent danger emptied his mind of everything else. The palace he reached by horse was dreadfully silent. Late at night, he roughly pushed aside the eunuchs who tried to stop him by citing his status and entered the front of Guest's quarters. Under a dim lamp, he saw his younger brother, who had come out of his room, startled by the commotion outside. Since they had reached adulthood and established their own factions, even private contact had almost ceased due to the eyes watching them. Facing Guest up close after such a long time, his face had shed its childhood softness and become that of a full adult possessing dignity. The moment he faced Guest, Yi Jae's gasping breath stopped. He didn't know what to say or how to say it, or how to package his inner feelings that had driven him to run here panting in the middle of the night. After staring at his brother for a long time with a flushed face as if he might collapse, Yi Jae painfully moved his frozen lips. ...The night air is cold, brother.