Kyon is interested in his classmate Haruhi Suzumiya, who introduces herself by saying she wants to meet time-travelers, aliens, etc. And Kyon gives her the idea of forming her own club, which she names the SOS Brigade.
Haruhi uses Mikuru to extort the Computer Research Society president and obtain a computer for the clubroom. Haruhi and Mikuru dress up in bunny costumes and hand out fliers promoting the SOS Brigade but are stopped by the school.
In an effort to alleviate her boredom, Haruhi enters the SOS Brigade into a baseball tournament. Tsuruya, Taniguchi, Kunikida, and Kyon's sister are recruited to fill out the team. However, the team is hopelessly inept.
Yuki states she is an alien, explains the Data Integration Thought Entity, and reveals that Haruhi has unconscious powers that could destroy and recreate the world on a whim. Haruhi recruits a transfer student named Itsuki to SOS Brigade.
A distant relative of Itsuki, Keiichi Tamaru, invites the SOS Brigade, along with Kyon's sister, to stay at his newly built island villa. Haruhi is excited at how the villa is a natural setting for a closed circle mystery.
Haruhi has Kyon add a logo of her design to the SOS Brigade website. A student named Emiri Kimidori asks the SOS Brigade to find her boyfriend, the Computer Research Society president, who has gone missing.
Kyon and Haruhi head outside to confirm Yuutaka took the boat, making him an obvious suspect in Keiichi's murder, and Haruhi spies a shadowy figure. Haruhi comes to a startling conclusion about the murder, but refrains from sharing it.
With winter setting in, Haruhi orders Kyon to pick up a heater. With him gone, she takes pictures of Mikuru in various costumes for the movie's DVD cover, Itsuki helps, and Yuki is left alone to read.
Kyon finds a mysterious letter in his locker directing him to come to the classroom, where Ryoko Asakura, the class president, confronts him. Also an alien, Ryoko attempts to kill Kyon in order to provoke a reaction from Haruhi.
On the day of the school's cultural festival, Yuki does fortune-telling, and Itsuki stars in a play, Mikuru and Tsuruya run a yakisoba café, and Kyon is recovering from his all-nighter working on the SOS Brigade's film.
Kyon is dragged into helping Haruhi investigate Ryoko's strange transfer. During the search, Haruhi tells Kyon about her childhood and how she became obsessed with paranormal phenomena.
One night, Haruhi's power is activated, trapping her and Kyon in a sealed reality at their school. While Haruhi investigates, Kyon is greeted by Itsuki, who tells him that Haruhi is creating a new world, retaining only Kyon from the old.
