Twin brothers Woo Jin and Bum Gyun encounter an alien as children, turning Bum Gyun dangerously paranoid as an adult in 2017. In 2037, Detective Kim and Chief Hong look for a way into a "crime-free" Smart Earth.

Woo Jin doesn't know what to believe when a disturbingly familiar student joins his class. The trust between Detective Kim and the Smart Earth employees is destroyed from the get-go.

With Bum Gyun still missing, Woo Jin teams up with Jung Yeon to look further into the suicides. Joon Hyuk proposes going to Normal Earth to access Park Jin Gyu's memories.

Woo Jin and Jung Yeon have a run-in with who they believe to be the culprit. Joon Hyuk and his team make a game-changing discovery about Bluebird.

Woo Jin becomes convinced of Jung Yeon’s otherworldliness, but she's reluctant to believe it. Detective Kim learns the true identity of Bluebird.

With new clues to investigate, Woo Jin expedites his search for Bum Gyun. In the future, Jung Yeon informs Detective Kim of someone who may know Woo Jin's whereabouts.

Woo Jin and Jung Yeon are disturbed to find out their fathers are not who they thought they were. Detective Kim must accept that Woo Jin's present may be different than what he'd imagined.

Woo Jin is cornered into helping Professor Han look for lost research. Detective Kim prepares for a possible meeting with the mysterious chairman of Human B.

When Woo Jin finds Bum Gyun, Professor Han starts to make his getaway. Detective Kim and Jung Yeon become two of Smart Earth's most wanted.

Professor Park realizes that the power lies in his hands now. Detective Kim receives new information about Woo Jin, but Human B is hot on his trail.

Woo Jin learns the truth about his father's research data, and Detective Kim learns the truth about what really happened to Woo Jin.

In the final episode, Woo Jin, Detective Kim, Jung Yeon, and their crew look for incriminating evidence against Park Dong Geun to take him down once and for all.