1448, the 30th year of Sejong's reign. The Ming dynasty's meddling into Joseon's domestic affairs goes to extremes and Sejong secretly plans to develop Singijeon, a rocket weapon upgraded from Goryeo's firearms technology. The Ming finds out and quickly dispatches assassins to attack the researh lab, but Choi Hae-san, the man in charge of the project, destroys himself along with the research materials to protect the weapon's secret. His daughter Hong-li (Han Eun-jung) barely escapes but loses the Singijeon Manual to the Ming assassins..