Circle: Two Worlds Connected - Season 1

Part 1 deals with Woo Jin and his twin brother Beom Gyun. Beom Gyun has been following the tracks of an alien they both saw when they were young. Part 2 is about a murder case that happens in supposedly a crimeless city, Smart City. Joon Hyeok enters Smart City without the care chip implant to his brain to solve the case and find his brother.

In Part 1, Woo Jin meets the woman who he suspects is an alien. And he gets a call from his brother that he had found the aliens' hideout and then loses contact with him. In Part 2, Joon Hyeok investigates Kim Min Ji case and realizes that her lost memory had been recovered.

In Part 1, Woo Jin and Jeong Yeon witness what is supposedly a suicide and from the body of the victim comes out a blue bug. They cut it open to find that it's a microrobot. In Part 2, Joon Hyeok almost catches Bluebird, but he fails as Ho Soo interferes. Ho Soo shouts out that he doesn't want to remember, and Joon Hyeok says he doesn't remember anything, so he doesn't know who he is.

In Part 1, Jeong Yeon gets attacked by a woman that claims that she's an alien and shows Woo Jin a picture of her with the toy star that he gave her 10 years ago. In Part 2, Bluebird leads Joon Hyeok to his past to find out who he is. It turns out he is Beom Gyun, and Bluebird is Jeong Yeon.

In part 1, After Woo Jin shows Jeong Yeon the photo of them together ten years ago, she gets confused about who she is. In part 2, Beom Gyun meets Jeong Yeon who had become Bluebird. Meanwhile, Ho Soo starts having nosebleed as he slowly recovers his memories.

In part 1, While digging for clues, Woo Jin finds a picture of Professor Han and his dad standing in front of Eunsung Psychiatric Hospital. In part 2, Beom Gyun meets Dong Geon. From him, he hears that the person who gave the presentation about the calming care system in the past was in his twenties, and he suspects that the chairman may be Woo Jin.

In Part 1, Woo Jin finds out that Professor Han is behind Beom Gyun's disappearance. In Part 2, Everyone who's been looking for Woo Jin is suspecting him to be the chairman of Human B as he did agree with Professor Han in the past that oblivion may solve PTSD.

In part 1, Woo Jin finds Beom Gyun in the house they used to live in when they were little. In part 2, the chairman of Human B asks to meet Beom Gyun. But it is discovered that the chairman is Minister Park Dong Geon. Beom Gyun asks where Woo Jin is.

In Part 1, Woo Jin realize that Beom Gyun is losing his memories. And at their old house, Woo Jin and Jeong Yeon finds something unexpected. In Part 2, Dong Geon tells Joon Hyeok that Woo Jin is alive. Joon Hyeok and Jeong Yeon go to a house guarded by Human B's security team and finds Professor Han there.

In Part 1, Dong Geon and Human B join hands and try to come up with a plan to get Woo Jin and Jeong Yeon. In Part 2, Jeong Yeon and Joon Hyeok go to Human B to find Woo Jin after finding out that their supercomputer won't work without Woo Jin. However, the supercomputer crashes.

Part 1: Woo Jin finds out that all the research data was destroyed. He plotted for the research data in exchange for Beom Gyun's surgery to remove the bug and gave himself up as collateral. Woo Jin finds out Dong Geon's motives. Beom Gyun's surgery goes well and Woo Jin escapes. Woo Jin gets into an accident while running away from Human B and Dong Geon. The person coming down the stairs turned out to be Woo Jin's clone. At first, Joon Hyeok denies that he's Woo Jin because of the real Woo Jin who died. But as the clone tells him his memory of the day he disappeared, he apologizes. He says he's sorry for letting him go there alone. 

Joon Hyeok suspects that Mayor Yoon has seen something that can be used against Dong Geon. Since Jeong Yeon can unlock his memories, they decide to take him out of Human B's hands and unlock it. And since Min Young is a doctor, she sneaks in to the hospital to take him out.