Kyon is an ordinary freshman high school student who, self-admittedly, has given up his fantasies of espers, time travelers, and aliens as he left middle school. However, sitting behind him is the beautiful, intelligent, and eccentric girl Haruhi Suzumiya, who in her class introduction blatantly states her singular desire in meeting aliens, time travelers, sliders, or espers. Interested, Kyon starts trying to make small talk with her before class, eventually leading to normal conversations with Haruhi. One day, after making a comment about Haruhi's displeasure with the available school clubs, he finds himself dragged into membership of the newly formed Spreading Excitement All Over the World with the Haruhi Suzumiya (or SOS) Brigade.

Haruhi quickly claims the Literature Club's room and its sole member, the silent bibliophile Yuki Nagato as property of the SOS Brigade and "voluntary arrests" the timid but cute Mikuru Asahina and the polite, smiling Itsuki Koizumi as the club's other two members. As the story progresses, however, Kyon finds that each of these supposedly "helpless victims" are actually agents of fantastic organizations who have been sent to monitor Haruhi, who they explain as having superhuman abilities of manipulating the universe. Haruhi's unawareness of her powers means that she unconsciously creates a new universe - one more to her liking - and attempts to switch over whenever she becomes bored or otherwise dissatisfied with reality. To prevent this, the members of Haruhi's club spend their time trying to keep their god-like leader entertained, hold her powers in check, and maintain the illusion of a normal life.

(From Wikipedia)