Origins.On board the ship Forward Unto Dawn , the artificial intelligence Cortana and Master Chief are stranded after the events of Halo 3. Cortana muses on her existence and what she has learned about the noble and ancient race known as the Forerunners. Cortana narrates past events: thousands of years ago, the Forerunners were a great civilization, but they came under attack by the parasitic Flood. The Forerunners underestimated the Flood, by which time it had spread, gaining the knowledge of the life it consumed. Though the Forerunners fought bravely, they eventually realized it was a futile fight. After trying other methods, they developed a weapon of last resort; an array of ringed megastructures called Halos that would destroy the Flood and their food supply—every sentient creature in the galaxy. While the Flood and Forerunner were wiped out by the Halo Array's activation, the Forerunners reseeded catalogued life throughout the galaxy. The second part of "Origins" follows the rise of human civilization. Humanity's exploration and colonization of other worlds coincides with the rise of the Covenant, a theocratic alliance of alien races that worship the Forerunners and reverse-engineer their technology. The Covenant launches a massive war of extermination against the human race. The events of Halo: Combat Evolved, Halo 2 and Halo 3 are summarized; a band of Covenant Elites ally with humanity to stop the Flood from spreading into the galaxy again, and the long war ends between human and Covenant. In the present, Cortana cryptically warns that the Halos are only one of the galaxy's many secrets. "Origins" was a chance to tell the story of the entire Halo universe in a clear fashion; many parts of the franchise had only been explored in what O'Connor called a "piecemeal" fashion.