Computer science major Sangwoo Choo lives his life according to three unwavering principles: reason, routine, and rules. He follows a meticulously organized schedule, drinks the same coffee every day, and sits in the exact same spot for every class. When his teammates contribute nothing to a group project, Sangwoo does what he believes is logical and deletes their names from the final presentation. His actions have unintended consequences for one teammate, popular design major Jaeyoung Jang, whose plans to graduate and study abroad are derailed because of the failing grade. Sangwoo does not see this as his problem and avoids Jaeyoungs repeated calls.

The story takes place at Hanguk University, where these two students from different departments computer science and visual design are forced to cross paths again. Sangwoo is developing a mobile game and needs a graphic designer. Through a mutual connection, Jaeyoung agrees to fill in for the role, only to discover that the rigid computer science student who ruined his academic plans is the very person he will now have to work alongside. Jaeyoung, who is known for his charming exterior but hides a hot temper, decides to get revenge by inserting himself into Sangwoos carefully ordered life and disrupting everything.

Despite their mutual disdain and clashing personalities that seem incompatible like oil and water, the two find themselves inexplicably drawn to one another. The novel provides deeper insight into their internal worlds than other adaptations. Sangwoo is portrayed as plainly neurodivergent, possibly on the autism spectrum, and he experiences the world through logic and rigid patterns. Jaeyoungs motivation for targeting Sangwoo is revealed to stem not just from anger over the failed class, but from a pre-existing crush he has harbored for years, combined with hurt that Sangwoo does not remember him at all. His harassment of Sangwoo, while still problematic, is thus contextualized as an immature response rooted in wounded feelings.

As they are forced to collaborate on the game project, their dynamic evolves from enemies to a slow-burn romance. Jaeyoung begins to learn how to understand Sangwoos neurodivergent perspective and adjust his own attitude if he truly wants to be close to him. Meanwhile, Sangwoo embarks on an internal journey to learn that it is acceptable to change his rules and routines to accommodate another person. Their relationship eventually becomes a purely physical affair to satisfy curiosity and needs, though Sangwoos inexperience with romance leads to complications. As the end of the school year approaches and Jaeyoungs study abroad plans loom, the two must seriously consider whether their relationship has a future beyond the campus. The title refers to Jaeyoung as a semantic error an unexpected flaw in the perfect, logical code of Sangwoos life that he must learn to debug.