The series features two parallel plots set in the years 2017 and 2037, both centered on twin brothers' struggle with the discovery and development of an advanced alien technology that could either be a boon or bane for the entire human race.

[a] By chance, Dr. Kim discovers Byul's secret: she had brought with her an advanced form of technology that can record, and even lock, memories and convert them into video.

In order to closely study this alien technology, Dr. Kim isolates himself from his family to work secretly on Byul in what he calls the "Beta Project."

In 2017, Woo-jin (Yeo Jin-goo), now a 21-year-old college student in neuroscience, feels that a series of suicides in his university is somehow linked to Bum-gyun (Ahn Woo-yeon), who has been searching for aliens, particularly Byul.

While in pursuit of the case, Woo-jin meets Han Jung-yeon (Gong Seung-yeon), a computer science student who, to his great shock, looks very much like Byul.