Human shouldn't develop a special part of anatomy called vomeronasal organ (VNO) - a peripheral sensory organ of the accessory olfactory system. The paired organs are located at the base of the nasal septum or in the roof of the mouth in most amphibia, reptiles and mammals as it only exists in myth for human.This part is usually found in animal to track their significant other. But Kyungsoo, being an exception, is blessed with the presence of the organ with a modification in its function. He can smell people. From the natural odour emitted by everyone, Kyungsoo can learn the true nature of someone without exchanged any words with that particular individual. Regrettably, humans are one insecure and paranoid creature. They are afraid to everything unusual and peculiar especially something that can harm their inner ugliness. 

So Kyungsoo stands alone to fight the paradigm of society and to prove his worthiness. Only that he lands on the wrong platform and trap himself further into mess. When he thought that he is alone all the way, a loud hyung rudely intruding his quiet life. And everything begin to change after that.