The Forerunner Saga is a trilogy of military science fiction novels by Greg Bear, based on the Halo series of video games.

Cryptum received mixed reviews; some critics liked the Forerunner culture and suspense that Bear created, but others disliked the characters, found the plot too slow, and concluded that the novel was suited only to existing fans of the Halo series.

Cryptum appeared on multiple bestseller lists after promotion on Halo Waypoint, a website that serves as a hub for Halo-related information.

"I basically said, we want someone of Greg Bear's caliber, that hard sci-fi grandeur that he handled so well in Eon and Anvil of Stars," O'Connor recalled.

[10] O'Connor said that the book is meant to have a "hard sci-fi" feel with a "hint of space opera, in the mold of Banks, Reynolds and Bear himself.

The young Forerunner Bornstellar Makes Eternal Lasting visits the human planet Erde-Tyrene (Earth), intent on discovering treasures left by the Precursors.

Humanity and their allies, weakened from fighting the Forerunners and a parasite known as the Flood, made a last stand on the ancient Precursor planet Charum Hakkor.

After their defeat, the Librarian saved the human race from extinction—they were instead stripped of their technology—and planted genetic commands known as "geas" in them, subconsciously allowing Chakas and Riser to lead Bornstellar to the Didact.

After crossing an ocean, the trio are found by a Lifeworker who accompanies them with several other humans and a giant ape named Mara.

While Catalog accompanies the Librarian, she tells it about the events that led to her becoming a Lifeshaper, and her growing split from the original Didact due to their differing opinions about humanity.

In the present, the original (Ur) Didact is discovered alive in a Flood-infected star system, having been captured by the Flood intelligence known as the Gravemind.

Formerly-dormant Precursor artifacts across the galaxy begin to reactivate, their immense power bolstering the Flood's already enormous forces.

In the confusion, the Ur-Didact uses converts human populations being stored on the nearby Halo into digital forms, and retreats to his mobile command installation, Requiem.

The Librarian sneaks aboard Requiem and confronts the Ur-Didact, who is using the essences of humans and his warriors to create an army of mechanical Promethean Knights to fight the Flood and ensure Forerunner supremacy.

The Librarian betrays the Ur-Didact and seals him in a cryptum, before returning to earth to oversee the conservation of its life forms before the activation of the Halo Array.

The Librarian passes her title of Lifeshaper to a subordinate, Chant-to-Green, and then sends Chant off to the lesser Ark with the planet's remaining humans.

The Gravemind sends ancient human essences to taunt the Librarian, revealing that the Forerunner's repository of information known as the Domain was a Precursor technology.

The Librarian realizes that the activation of the Halo Array will mean the destruction of the Domain, and that it will condemn the Ur-Didact to spend the eons to come in complete silence, dwelling on his own rage and madness.

At the lesser Ark, the IsoDidact activates the rings while the remaining Forerunners fends off Mendicant Bias' fleet, stopping the Flood.

The novels in the Forerunner Saga were promoted with author events and meetings with 343 Industries personnel, excerpts published in the weeks before release, and giveaways.

[25][26][27] Cryptum was the first Halo novel to release in hardcover, in addition to the paperback format, with a total initial print run of 300,000 copies.

[28] Following its release, Cryptum reached number 22 in the New York Times Best Seller List in the Hardcover Fiction category.

Dr. Nigel Seel of sciencefiction.com called it tired, unoriginal and boring, saying, "It's hard to care about the flimsy characters, the plot is wearily over familiar, the hero is passive throughout and overall, not enough happens."

"[32] Hilary Williamson of Book Loons also considered Cryptum appealing only to Halo fans, but praised Graham's narration.

[34] Jason Hamilton of Story Hobby also praised the novel; he complimented Bear's creation of a completely different culture to humanity and his balance of providing the reader with enough information to maintain interest without letting on too much and ruining the suspense.

[35] Halo: Primordium was on the New York Times Bestseller List: Hardcover Fiction for the week of January 7, 2012 at number seventeen.