In Our Prime

A genius mathematician, Lee Hak-sung, defects from North Korea in pursuit of academic freedom. To conceal his identity and past, he takes on the role of a security guard at an elite private high school, where only the top 1% of gifted students are admitted.

With his cold and stern demeanor, Hak-sung becomes the most avoided figure on campus. However, his life takes an unexpected turn when he meets Han Ji-woo, a struggling high school student who has given up on math. After discovering Hak-sung's true identity, Ji-woo persistently begs him to become his tutor.

As Hak-sung teaches Ji-woo not just how to find the right answers, but how to navigate the process of problem-solving, both of them experience an unexpected transformation in their lives.

• Choi Min-sik as Lee Hak-sung, a school security guard and defector from North Korea
• Kim Dong-hwi as Han Ji-woo, a student who asks Hak-sung to teach him math
• Park Byung-eun as Kim Geun-ho, a math teacher
• Park Hae-joon as An Gi-cheol, agent of the National Intelligence Service who monitors Lee Hak-sung
• Jo Yun-seo as Park Bo-ram, Ji-woo's classmate
• Tang Jun-sang as Lee Tae-yeon, Hak-sung's son^[5]
• Kang Mal-geum as Han Ji-woo's mother^[5]
• Kim Hee-jung as Park Bo-ram's mother
• Joo Jin-mo as Oh Jeong-nam, a mathematician who participated in an international math competition with Hak-sung
• Kim Won-hae as Park Pil-ju, a North Korean defector and Economics professor