Circle (TV series)

Circle (Korean: 써클: 이어진 두 세계) is a 2017 South Korean science fiction TV series. Its main cast includes Yeo Jin-goo, Kim Kang-woo, Gong Seung-yeon, and Lee Gi-kwang. The story unfolds across two connected timelines—2017 and 2037—and revolves around twin brothers grappling with the discovery and development of an advanced alien technology that could either help or harm all of humanity. The series aired on tvN for 12 episodes, each broadcast at 23:00 KST on Mondays and Tuesdays from May 22 to June 27, 2017.

The narrative begins in 2007, before the main events. Eleven-year-old identical twins Kim Woo-jin and Kim Bum-gyun, along with their neuroscientist father Dr. Kim Kyu-chul, witness the arrival of a female humanoid alien. Out of pity and curiosity, the family takes her in and adopts her. Woo-jin names her Byul. Dr. Kim later discovers that Byul brought an advanced technology capable of recording, locking, and converting memories into video. To study this technology closely, he isolates himself to work on the "Beta Project" and never returns home. Bum-gyun believes Byul has taken their father captive, while Woo-jin thinks their father abandoned them.

In 2017, Woo-jin, now a 21-year-old student, suspects a series of suicides at his university are linked to Bum-gyun, who has been searching for aliens—especially Byul. While investigating, Woo-jin meets Han Jung-yeon, a student who looks exactly like Byul. She is also looking into the suicides, which she believes are actually murders.

In 2037, South Korea is split into two zones: Normal Earth, a heavily polluted and crime-ridden area, and Smart Earth, a clean, peaceful, and crime-free city. Kim Joon-hyuk, a Normal Earth detective, tries to enter Smart Earth to investigate a case involving twin brothers who went missing in 2017. As he does so, he uncovers the dark truth behind Smart Earth's supposed lack of crime.

Each episode except the last has two parts: "Part 1: Beta Project" (set in 2017) and "Part 2: A Great New World" (set in 2037). The two plots merge in the twelfth and final episode, titled "Circle: One World."

The main cast includes Yeo Jin-goo as Kim Woo-jin (in the Beta Project segments) and as Circulate 3 (in A Great New World), with Jung Ji-hoon playing young Woo-jin. Woo-jin is a 21-year-old second-year student at Handam University of Science and Technology.