"The Expanse" is the fifty-second episode of Star Trek: Enterprise, the twenty-sixth episode of the second season, and the Season Two finale. The episode launched a change of direction for the series, starting with a cataclysmic attack on the Star Trek version of Earth and introducing a new alien foe, the Xindi.This episode set the foundation for the season-spanning Xindi story arc, encompassing all of Season Three and the first three episodes of Season Four. The story line continues in the Season Three opening episode, "The Xindi". Source: Wikipedia (en)