This Synopsis was written by me.
Kyon was just an average guy, a bit lazy and apathetic, but a good guy nonetheless. Most of the days in his life were pretty uneventful, and he figured his days upon entering high school would be about the same. That's what he thought, until he met her…Haruhi Suzumiya, an intelligent and talented but extremely eccentric girl who's completely bored with everyday life. So much in fact, that on the first day of school, she announced to the class that she has no interest in "ordinary humans" and that any aliens, espers, and time travelers should come and see her. Half-jokingly, Kyon mentions to Haruhi that since she's so bored with everything, even with the variety of clubs at school, why not make her own club? But little did Kyon realize that upon hearing that idea, Haruhi would literally drag him along into her newly made-up, and rather unique club "Save our world by Overloading it with fun Haruhi Suzumiya's Brigade" (or "SOS Brigade" for short). Haruhi made it the SOS Brigade's goal to find and investigate all manner of mysterious and unexplainable events or anything else out of the ordinary. And in addition to Kyon, she drags three other members into the Brigade; shy and polite upperclassman Mikuru Asahina, quiet and stoic bookworm Yuki Nagato, and cheerful transfer student Itsuki Koizumi.
As if putting up with Haruhi's eccentric antics isn't enough, the real shocker comes when Kyon learns from Yuki, and later Mikuru and Itsuki tell him their side of the story, that they as well as Haruhi are not ordinary humans. In fact, the three of them are the very beings that Haruhi is seeking; Yuki is an alien, Mikuru is a time traveler, and Itsuki is an esper. They tell Kyon that they were each sent by their respective leaders/organizations to secretly observe Haruhi. Why Haruhi? Because she has the amazing ability to unknowingly alter the world and events around her to suit her own desires (evidence in the fact that an alien, esper, and time traveler were indeed brought to her just as she wanted). But although they have different views on the exact nature of Haruhi's power, they agree that all this must remain a secret from her for fear of what she might do if she realized her own powers. If Haruhi gets too bored or upset, she may inadvertently use her powers to greatly alter reality, sometimes with devastating consequences. So in order to keep Haruhi from getting "melancholy" and using her powers, Yuki, Mikuru, Itsuki, and unwittingly Kyon as well, take on the task of not only observing Haruhi but also finding ways to keep her entertained and humoring her in the many crazy and often outrageous activities she comes up with for the SOS Brigade. Many times, often as a result of Haruhi's power, strange and unusual events do occur around them, but somehow they always manage to keep it a secret from her. So Haruhi continues her pursuit of mysterious and unexplainable phenomenons through the SOS Brigade, never realizing that the people and events around her, as well as her own existence, are more extraordinary than she could ever imagine!