Halo: What Is the Flood in the Season 2 Finale?

This Halo article contains spoilers.

It’s not long after Halsey, Miranda, and Kwan discover the ancient Forerunner device that ONI scientists and UNSC officers start chomping down on each other. They’ve been infected with the strange spore contained inside the device and now everyone, including Admiral Parangosky and Laera, are lunch. What the hell is happening in the Hahlo season 2 finale?

It’s time to meet the Flood in the alternate Silver Timeline. In a big twist, they’ve arrived much earlier than in the game the show is based on, already spreading beyond the Halo ring long before Master Chief and Cortana even have a chance to stop the alien parasite from consuming everything in its path. It’s perhaps the show’s biggest deviation from the source material and will likely mean the Flood storyline plays out much differently on TV than it did in the Halo trilogy. But at the same time, from what we see in the Halo season 2 finale, the basic function of the Flood in the Silver Timeline seems to remain the same: infect anything and everything until there’s nothing but the Flood left.

First introduced in Halo: Combat Evolved, the Flood quickly become the main threat of the original trilogy of games, as it begins quickly consuming both the humans and the Covenant once its accidentally freed from its quarantine on the Halo ring. Once unleashed, the Flood doesn’t just take over the Covenant capital world of High Charity but it eventually makes its way to Earth. By the end, what’s left of the UNSC and ex-Covenant forces who have broken off from the larger enemy faction must work together to stop the Flood for good.

Although the Flood might seem like its made up of mindless zombie-like creatures, this species is actually highly intelligent and connected through a hivemind known as the Gravemind that grows more potent and powerful the more it consumes. The Gravemind essentially commands all Flood forms during an outbreak. You should probably expect to eventually meet a version of the hivemind on the show.

Sounds terrifying, right? To make matters worse, we learn the Flood was actually the reason the Forerunner race that preceded both humanity and the Covenant went extinct in the first place. Millennia before the events of the game, the Flood succeeded in spreading itself throughout the galaxy and the Forerunners created the Halo rings as a failsafe to prevent the parasite from spreading further. The Forerunners were forced to activate the rings, wiping out all sentient life, including themselves, disrupting the Flood’s food source long enough for them to die out, aside from a few specimens kept quarantined inside the rings themselves.

Because the Forerunners insisted on keeping these specimens a secret, the Flood once again became a threat thousands of years later. In the first game, the Covenant accidentally unlocks a Flood containment facility on the Halo ring, awakening the long-dormant survivors. When the UNSC later stumbles on the site, they discover first hand how deadly this parasite can be.

The Flood exists in a variety of forms, the smallest being dust-sized spores that can be unwittingly inhaled by potential hosts. Before finding a host, the Flood can also grow from tadpoles to pods (the primary form of infector, hunts hosts on the ground) to seeders (deploys airborne spores for infection through tentacles). Once they find a being to infect, the Flood can then transform the host’s biomass into whatever the Gravemind needs, with most forms being large, hulking monstrosities.

No matter what form they come in, the Flood pose a great threat to both the Covenant and the UNSC. With the ability to absorb and assimilate their hosts’ memories and intelligence, this parasitic organism is a formidable enemy for all lifeforms. Both Master Chief and Makee will learn that soon enough.

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