The end of the Human-Forerunner War, along with the political fight afterwards that led to the Exile of the Didact, spurred much debate within Forerunner leadership about the right course of action to defend civilization and the galaxy against the Flood, should they return. In an attempt to learn more about their origins, the Librarian chartered a mission to Path Kethona (Large Magellanic Cloud to humanity), where it was thought the Flood originated.
Upon arriving in the galaxy, the Librarian and the rest of the crew discovered a planet inhabited by descendants of ancient Forerunners and what they could only describe as a biological Domain, where all their historical knowledge was kept. It was through their interactions with the Forerunner descendants and the biological Domain that the Librarian discovered the truth about the Forerunner-Precursor War ten million years prior and the shame those ancient Forerunners faced after the destruction of their makers. Though the Librarian returned seemingly without knowledge of the Flood’s origins, it was only later that she was able to piece together this information with what the IsoDidact would learn later from the Primordial and determine that the Precursors were the source of the Flood.