EVeryone in the world has a conscience, basically a Jiminy Cricket on your shoulder telling you what you should and should not do. They can't be seen with the human eye, but they are no doubt real. They whisper in your ear and make you do the things you do. Kyungsoo's conscience makes him academically on top and has never been in trouble a day in his life. He may not be very popular, but him and his conscience never really paid attention to that since they were both shy. On the other hand, loud and outgoing Jongin, or more often known as Kai, is all about it. He loves to socialize, and hates studying. 

One fateful day, they both end up blacking out and waking up the next day. All seems normal until kyungsoo starts getting know his deskmates, and Kai speeds through his math test like it was nothing. Their consciences have switched. And as time goes on they think they'd rather be unconscious than have any at all.