Before Crisis's story begins shortly after the ending of the war between the Shin-Ra Electric Power Company and the Wutai tribe, a conflict mentioned in passing during Final Fantasy VII. With Wutai defeated and the people of the world now dependent on their Mako Energy and materia, Shin-ra finds itself the dominant economic, military and political power in the world. But there are those who remain dedicated to the destruction of Shin-Ra, chief among them being the newly emerged insurgent movement known as "AVALANCHE". Before Crisis focuses on this conflict between Shin-Ra and the original AVALANCHE group, which began six years before the events portrayed in Final Fantasy VII, and lasted up to the time immediately preceding the events that took place in that game. In contrast to Final Fantasy VII, which was focused mainly on the viewpoint of the second incarnation of AVALANCHE, Before Crisis centers around the Shin-Ra Company's Turks, with AVALANCHE serving as the game's main enemies.

The game unfolds through a series of "episodes." Because of the subscription-based nature of the game, the game's story unfolded over a period of time.

( Reference: http://www.square-enix.co.jp/mobile/bcff7.html )