Ace NIS agent Jung Hae-seong is demoted after a mission failure. He goes undercover at a high school to locate King Gojong's missing gold, meeting his teacher Oh Soo-ah, who sees him as her lost first love, stirring old heartbreak.

• Seo Kang-joon
• Jin Ki-joo
• Kim Shin-rock
• Kim Min-ju
• Yoon Ga-i
• Kim Young-ah
• Lee Hyun So
• Yun Chae-bin