A little boy falls in love with a big girl.
Unable to confess, the littlest detective is gifted by a deus ex machina with the girl's phone number. Never minding the strange area code, he immediately calls her, and is overjoyed to find out that she has a crush on him as well.
But, the next day, when he recounts the previous day's confessions to the girl, she only looks at him with a perplexed expression. After some investigation, he finds out that the girl he called is not the same girl he fell in love with. In fact, she doesn't exist in this universe at all. She is the girl's alternate universe counterpart, who has fallen in love with the MC's own AU self, who too is blissfully unaware of her crush and is fully grown.
Hijinks ensue as the two strike up a deal to give each other their darkest, most private secrets in order to equip the other with the weapons they need to conquer the heart of their other selves. While the two chase their respective loved ones, DRAMA ensues as they begin to fall in love with each other instead and question the NATURE of DETECTIVES.