As to the nature of the Flood … In every natural circumstance, living things engage in competition. This is a prime directive for those who uphold the Mantle: it is not a kindness to diminish competition, predation—even war. Life presents strife and death as wel as joy and birth. But Forerunners in their highest wisdom also knew that unfair advantage, mindless destruction, pointless death and misery—an imbalance of forces—can retard growth and reduce the flow of Living Time. Living Time—the joy of life’s interaction with the Cosmos—was the foundation of the Mantle itself, the origin of al its compel ing rules.

And the Flood seemed to demonstrate a tremendous imbalance, a cruel excess of depravities. Certainly humans and San’Shyuum had felt that way.

The Flood first arrived from one of the Magel anic clouds of stars that drift just outside the reaches of our galaxy. Its precise origin was unknown. Its first effects upon human systems in the far reaches of our arm of the galaxy were subtle, even benign—so it seemed.

Humans suspected it was conveyed on ancient starships, clumsy in design but completely automated. The ships had neither passengers nor crew, and carried little of interest but uniform kind of cargo—mil ions of glassy cylinders containing a fine, desiccated powder.

Humans found wreckage of the ships on uninhabited and inhabited worlds alike.

The cylinders were careful y examined, using the most stringent cautions, and their powdery contents were analyzed and found to be short-chain molecules, relatively simple and apparently inert—organic, yet neither alive nor capable of life.

Early experiments demonstrated the potential for psychotropic effects in some lower animals, but not in humans or San’Shyuum. The primary animals affected by the powder were, as it turned out, popular pets in human societies: the Pheru, lively and gentle creatures first found on Faun Hakkor. Very smal quantities of the powder induced changes in the Pheru that improved their domestic behavior, made them more affectionate, not so much docile as cleverly charismatic. Soon enough, on an emerging black market, outside the control of human governments, Pheru treated with these rare powders commanded a very high price. San’Shyuum at this point also adopted Pheru as pets.

For centuries, dozens of human and San’Shyuum worlds bred and powdered these animals—without il consequences. No researcher suspected the long-term effects of the powder, which attached itself to key points in the genes of Pheru and began to change them … while at the same time improving their behaviors.

What would soon become the Flood first manifested itself as a peculiar growth found on roughly a third of al Pheru treated with the powder. A kind of loose, soft fur grew between the shoulders of the pets. It was regarded by breeders as a natural mutation, even a pleasant variation.

The sensuous quality of the fur particularly impressed the San’Shyuum, who crossbred these specimens.

Other Pheru were soon found grazing on these companions, consuming their fur —and on occasion even consuming the animals themselves. Pheru were natural y herbivores.

This seemed to activate some sort of biological timer, a signal for expansion.

Within a very short time, the Pheru were producing far less attractive growths.

Flexible striped rods sprouted from their heads, which in turn were also consumed by fel ow Pheru—causing abortions and unnatural births.

There was no cure. But this was only the surface of the growing infestation.

The Pheru were soon past recovery. Humans and San’Shyuum dispatched their pets with regret—and puzzlement, for these first stages were beyond their biological understanding. Most researchers believed the Pheru had simply become overbred, overspecialized. A few were even returned to their native habitat on Faun Hakkor.

Then—humans began to manifest the growths. Some humans, it seemed, fancied Pheru as food. These humans became vectors. Whatever they touched was also infected, and in time, what they discarded—limbs, tissue—could also spread infection.

Thus began the Flood.

The plague soon spread from human to San’Shyuum, human to human, but rarely from San’Shyuum to human—altering their behaviors without yet changing their outward appearance. The infected humans combined their resources to force other humans to become infected—usual y by cannibalism of a sacrificial individual, induced to grow to prodigious size before being consumed while stil alive.

By this time, dozens of worlds were ful y infested and beyond saving.

Humans and other animal species began to reshape themselves into other varied and vicious forms equipped to maim and kil —and consume, absorb, transform.

The infected worlds and even entire systems were quarantined. Many of the infected escaped, however, and spread the plague to hundreds of worlds in fifteen systems.

Humans were the first to recognize the extreme danger. And this was where the ancient captive in the Precursor prison came into the story. Humans had discovered how to communicate with the captive—but only for seconds or minutes at a time. The earliest researchers tried to use it as a kind of oracle, asking the answers to vast and difficult questions of physics and even morality—al of which drew out confused or useless responses.

But final y a set of questions were prepared and asked. They asked about the Flood.

And what these humans received as answers traumatized them so thoroughly that many committed suicide rather than continue to live with their knowledge.

In time, as a kind of defense, access to the captive was reduced, then cut off completely. The human timelock was added. Communication ceased.

Most humans came to believe that the captive was an ancient aberration and had been imprisoned by the Precursors for just cause, and that its prognostications, if they were such, were nonsensical, even mad.

Humans at the height of the Flood’s ravages were pushed to an unexcel ed bril iance.

They found a cure. (Here I detected in the documents the admiration of the Lifeshaper herself.) Sacrifice yet again. Ful y a third of the human species must be themselves altered, placed in the pathway of Flood infestation, and fight fire with fire by infecting the Flood itself with a destructive set of programmed genes.

The Flood had no defense; most of it died off. A few ships carrying the last of the Flood escaped and left the galaxy once again, destinations unknown.

By the time of this heroic struggle, humans were fighting Forerunners as wel .

Humans were desperate. Their desperation made them cruel. They needed new worlds, uninfected worlds—and took them. Cruelty and apparently irrational conquest and destruction forced Forerunners to react decisively.

This double war was the source of the Didact’s shame, though how he would have altered his conduct, had he known, was far from clear.

Human forces were eradicated and human-occupied worlds were reduced, one by one, until the battle of Charum Hakkor destroyed the last human resistance. The San’Shyuum had already surrendered. None were found to be infected by this so- cal ed plague. Al the powdered and infested specimens of the Pheru were long dead, destroyed. The original vessels that had carried the glass containers were also destroyed, perhaps in the perverse human wish that Forerunners would face a similar infestation and be unprepared.

Many Forerunners, in fact, regarded the entire story of the Flood—for that was the name humans gave to this spreading infestation, this intergalactic disease—as a fabrication designed to absolve humans and San’Shyuum of blame.

The rest of the story I knew or had deduced, and my knowledge matched the Didact’s. The Librarian was al owed to preserve some human specimens, and to preserve the memory traces of many others, a procedure regarded with much dissent and disgust by orthodox observers of the Mantle.

But the possibility of the return of the Flood initiated the events which shaped Forerunner history up to my own time. And most of it—nearly al of it—was kept secret by the Master Builder and his guild, my father included.

Only a few sympathetic councilors were ful y informed.

Thus began the conflict with the Prometheans. The Didact proposed vigilance and research—and upon any return of the Flood, however it might manifest, a systematic isolation of infected worlds and, if necessary, immolation. He proposed establishing fortress worlds—Shield Worlds—across the Forerunner-dominated portions of our galaxy, to monitor potential outbreaks and be prepared to fight them with pinpoint precision and minimum destruction.

Others had more ambitious solutions. The Didact and the Prometheans faced off against the most extreme faction of Builders, now in complete control of the Council. This faction saw both an opportunity to create ultimate weapons against such a threat, and a way to maximize and make permanent their political power at the same time.

Thus my father and the Master Builder began to design a series of instal ations, far fewer in number than the proposed Shield Worlds—what would become the Halos.

By radiating a powerful burst of cross-phased supermassive neutrinos, these instal ations were capable of destroying al life in an entire star system. Properly tuned and powered, they could do more than that—they could kil al neurological y complex life across whole swaths of the galaxy.

The extreme faction won. Fear commanded the Council, and the Council listened.

The Didact lost his political battle and was forced into exile.

Over the next thousand years, twelve such instal ations were built. Their point of construction was far outside the galaxy, on a superior instal ation known as the Ark.

It acquired that name because of the growing backlash of influence rising from Lifeworkers, and in particular from the Lifeshaper herself—the Librarian.

She insisted that not to make provisions against the ultimate use of the Halos was blasphemy against the Mantle. Lifeworkers had their own kind of influence. If they stood down, al medical efforts could cease. The Master Builder saw that giving in to her demands was less expensive than fighting her.

And so, the Librarian was al owed to gather specimens and re-create their ecological conditions on the Ark itself—even as the Ark finished and transported the first Halos, utilizing a powerful variety of locked-point slipspace transit cal ed portals.

The instal ations had been dispersed. The Halo tested at Charum Hakkor had been fired at very low power, acting as a test bed. That had been an authorized use.

But then, a second Halo had been used to punish the San’Shyuum. With horror, I realized that what I had witnessed had been only the beginning—and that the San’Shyuum worlds, after our brief, traumatic visit, had been reduced to the awful condition of biological blandness we had seen on Faun Hakkor.

The Council had not authorized this use. The Master Builder had exceeded his authority. He had been accused even by his col eagues of blasphemy against the Mantle, and a crime against nature.

What the Didact could not understand—at the time of my mentoring—was why the Librarian had chosen this moment to gather specimens from the San’Shyuum, taking the risk of provoking their rebel ion—and the Master Builder’s wrath. I found that answer in the Council records, with the help of my expanded and liberated ancil a.

Three hundred years before, the Flood had returned. It had been discovered in new and unexpected forms on worlds resettled by Forerunners after the war.

* * *

I was caught in a twisted knot of contradictions. Faced with the reality of the Flood, I couldn’t help but think that the madness of those who had manufactured the Halos and set them loose might be the right course. A solid goal, a solid plan! Extreme measures against an extreme enemy. Fighting for survival against a shapeless threat. The Mantle be damned—survival and our way of life was at stake!

It al seemed eminently rational. I almost began to believe that it was the Didact who was mad, and possibly these young councilors, and not the Master Builder or my father.

Final y, in fury and frustration, I divested myself of my armor, deliberately cutting off contact with the ancil a, whom I thought had failed me or misled me again— And I slept.

If I was in search of peace and certainty, that was my mistake. The Didact’s actual memories—parts of them—final y blossomed within me.

The arena was equipped with walkways— I saw vividly, from his point of view, the Didact exploring the walkway around the intact, sealed cylinder below.

Ten thousand years ago.

The Didact walked alone around the dome-shaped cap, contemplating whether or not he should activate a human device … something smal , designed for a human hand and fitting like a toy into his own palm: a way of communicating directly with the creature within the cel .

Something manufactured by humans … pushing through Precursor technology. How was that possible…?

Many questions flashed through the Didact’s mind, and with difficulty I separated them from my own. Was this actual y a Precursor, as the humans had at first believed? Or was it something manufactured by Precursors—possibly a strange, distorted sibling to both Forerunners and (the Didact was reluctant to consider this) humans?

Precursor, sibling, or ancestor to … what?

The Didact manipulated the device. The cap over the cylinder became transparent to his eyes, and he saw what lay within.

The cel contained, in temporal suspension, a genuine monster: a large creature with an overal anatomy like a grossly misshapen human, though possessed of four upper limbs, two degenerate legs, and an almost indescribably ugly head—a head shaped remarkably like that of an ancient arthropod seeded long ago on a number of planets, presumably by the Precursors, and known to some as a eurypterid. A sea scorpion.

Oval, faceted, slanted eyes bumped up from the front of its low, flat “face.” And from the rear of the head, a long, segmented tail descended the spine, ending in a wicked barb two meters in length.

* * *

A chime pul ed me up short. Disoriented, shivering, unsure who or even what I was, I looked around my cabin, saw my armor slumped in one corner and a ship’s ancil a blinking rapidly in another.

We had final y reached the capital. Even with the extended journey, there had not been enough time to ful y integrate. Without the Domain, integration might forever elude me, and inside, I would always be a fragmented jumble.