Byun Baekhun, an average college student who didn't really do much out of his comfort zone is forced to accompany his roommate, Jongin, to the bar for a night. When Jongin leaves him for his crush Kyungsoo, Baekhyun is left to go home with a stranger. Little did he know this stranger was his English professor. Park Chanyeol. #1 in beakyeol

They are going so well. Chanyeol spends every day seeing the light sparkle in Baekhyun's eyes and watching the love of his life return to his old self. He doesn't think anything can happen to Baekhyun, or come in between them, especially when he promises himself he will let nothing hurt Baekhyun ever again. Especially when he sees that the way Baekhyun looks at him is different from the way Baekhyun looks at everyone else. "Do you love me?" He asks. Baekhyun opens his mouth, but he never has the chance to answer. "Baekkie?" Joo-hyung returns, and this time, it is for a completely different reason.

Thousands of years ago, human evolved into two distinct intelligent species. Once, they coexisted together for hundreds of years. Once, they lived in harmony together. Then, one day, it all changed. No one knew how, and no one knew why. 30 years ago, one of the intelligent species spiraled out of control, turned aggressive and murderous, and killed. It wasn't war - it was pure slaughter. These killers were then named the Monsters. Two years after the Mass Attack, the other intelligent species began fighting back, using their weapons and research, targeting the Monsters' weaknesses so they would be unable to play to their strengths. Although the Monsters were more powerful, there were less of them. This movement of retaliation was called the Movement of Assassination, and it lasted four years. The surviving victims escaped and found refuge in a place in which only the richest of them live, inside an island bubble beneath the deepest waters of Earth, a place in which little to no Monsters thrived. It was a man, a clever and well-known man, that led them towards the island bubble which was named SQUAOII. He then became a legend, and went by the name "FREQSE". These surviving victims that Freqse led were called the Lucky Ones. Since then, the Lucky Ones lived in harmony inside SQUAOII, with all the Monsters they found executed or taken in for investigation. Freqse used his knowledge and power to build a laboratory to investigate the origins of the MAMA War, and what made the Monsters turn into Monsters, in an attempt to bring back harmony between these two species again. Ever since, this laboratory, called the EX'ACT Lab, had become the centre of admiration and attention. Ever since, no one inside SQUAOII, aside from scientists, has ever seen, or remembered seeing, what a Monster looked like.

Four strangers. Two Weddings. A fated switch. A millionaire's son isn't supposed to marry a gang leader. A gang leader's son isn't supposed to marry a Minister's son. Right? Bad is to be forced into marriage. Worse is to marry the wrong man. Worst is to fall in love with that wrong husband. AN: This is an EXO version of The Perfect Mistake.

The day when Byun became Park is also the day Baekhyun's life will change.