The Pheru came from Faun Hakkor, in the same system as Charum Hakkor, one of the key centers of human culture, as well as an amazing collection of massive Precursor artifacts.

Centuries before the beginning of our war, the mutated Pheru entered a new phase and produced spores that infected their masters with the first stage of the Flood. The infection spread rapidly, evolving quickly in its new hosts and weakening humans so severely that early Forerunner victories came with surprising ease.

Humans were, in effect, fighting on two fronts.

But within decades, that situation changed. Humans surged back. Their strength redoubled. Our fleets came upon strong, healthy human populations residing in Flood-infested sectors of the galaxy, apparently unmolested. Humans had obviously found a way to immunize against the Flood, or had developed a natural resistance—or possibly even found a cure.

Yet despite this rebound, Forerunners had taken sufficient advantage of the earlier, troubled period to organize our forces and distribute them to key positions, great in both strength and strategy.

My husband’s fleets and warriors made tremendous gains.

The Flood no longer seemed to infect humans, but along the galactic margins, in many other systems, it held its awful sway over thousands of worlds. Wherever the Didact’s forces came upon pockets of infection, they burned them out—cauterized them by sheer firepower. The Flood seemed to be quelled—for a time. The Didact and I knew these piecemeal efforts should not have been enough. Lifeworkers calculated that given its virulence and adaptability, the Flood should have overcome our entire galaxy within a few hundred years.

Yet before our eyes, even as humans were being defeated, the Flood was evaporating like frost on sun-warmed ground. It seemed to deliberately retreat, as if it had established a pact with humanity and was sensitive to their change of fortune. Forerunner fleets soon squeezed humanity into a few redoubts. Charum Hakkor held out to the very last.

It seemed for a time that our two greatest enemies were being defeated. But Forerunners could not afford complacency. We knew what the Flood was capable of. There was an overpowering conviction, and not just in the Old Council or among the Builders, that it would return with renewed virulence. And we had no immunity.

We desperately needed to learn how humans had survived the Flood. Captured humans could not be forced to divulge these secrets. Analysis of dead humans revealed little. But the Old Council became convinced a vaccine or cure existed.

And yet they had ordered the destruction of the human race. It was obvious this contradiction had to be resolved.

Already some Builders were laying their own plans for a solution if there was ever a resurgence of the Flood. The culmination of those plans would come thousands of years later, and would be called Halo. Even so, it seemed appropriate—and politically expedient—for a Lifeworker to be put in charge of Flood research.