The game is split up into three cases, each with its own storyline and scenario. The concept is that various characters have been put on trial for crimes they claim they are innocent of. You play Haruhi, as she defends them.

The cases are split up into two phases. The investigation phases, where the player explores the school as Kyon, talking with other characters and gathering evidence, and the trial phases, where the player must defend their client in court as Haruhi.

[From Haruhi Wiki]