In Halo 3, one cinematic states that Cortana has found a solution to the Flood other than the Halo rings. Master Chief wants to go to the Ark to pursue this solution (and is told that stopping the rings is first priority).

According to this question, the Gravemind also wants to know what this solution is.

However, by the end of the game, as far as I can tell it hasn't been mentioned again (tvtropes warning), and the game ends with the Flood still presumably at large.

Did I miss something? What was this solution? Does it get mentioned again in a later game? (For bonus points, what did happen to the Flood elsewhere; are they just being "contained" using "conventional" means?)

  • Without much to back it up, I've assumed that the plan was what happened: Cortana has reason to believe the Gravemind will head to the Ark, either because Truth is there or he was baited by her message, and that the new Halo can be used to wipe out the Flood there. She certainly picked up on Master Chief's plan quickly enough: "do you have it?" is immediately interpreted as the Index.
    – Nolimon
    Commented Jul 27, 2021 at 14:54

1 Answer 1


Her solution isn't to activate the Halo rings, but rather to hoax Gravemind into following her to the Ark, which is far removed from Milky Way. Her recording to Master Chief Sierra 117 indicates that she knows that Gravemind is listening to her channels or monitoring (or at least trying to monitor) her affairs and any data she moves, edits, or produces on the centralized computation structures of the compromised ship:

... I can't tell you everything. It's not safe. The Gravemind...it knows I'm in the system.

– Cortana, Chapter 6: Floodgate

Once rescued, and with Gravemind chicaned, Cortana could then use the Index from the Ring in Halo: Combat Evolved to prematurely activate the re-constructing Ring at the Ark to destroy it (the Ark and the new Ring itself), the Flood, and whatever Covenant contingencies within the vicinity, concurrently, without activating operative Halo rings spread throughout the galaxy.

Cortana: "The Activation Index from the first Halo ring. A little souvenir I hung onto... just in case. Got an escape plan?"

Master Chief: "Thought I'd try shooting my way out – mix things up a little."

Chapter 9: Cortana

It's not clear why the original Index works on the renewed ring.

  • I guess what's not clear here is how this "solves" other Flood infestations. Are we supposed to assume they become a non-issue once Gravemind is gone? It felt to me like activating the new Halo was a case of "new problem, new plan". Are there any out-of-game sources that back up this interpretation?
    – Matthew
    Commented Jul 27, 2021 at 19:34
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    "It's not clear why the original Index works on the renewed ring." Could just be a master key? The "safety" precaution is that only a forerunner or the "Reclaimer" can operate it
    – Ben
    Commented Jul 27, 2021 at 23:28
  • @ben good point. but after what happened with the original one, you'd think that the sentinels or their leadership would take precaution. if a premature firing of the installation was known to cause a self-destruction, then the key, or copies of it, might still be floating around; anyone with the Index who arrives at the installation before it's finished could conceivably weaponize it in this unintended fashion. Commented Jul 28, 2021 at 16:55
  • @mathew cortana and the chief may view it as a solution, but it's a temporary fix. flood matter and spores that survive will invariably form into a new proto Gravemind and over time spread. the forerunners knew this, and the inevitable return somehow, which is why they kept live samples in order to study them. and then the Covenant released them at 8, which led to massive amounts of infection. I'm not sure where the Gravemind came from, though, he seemed to just be selected and then fed more and more hosts in the lib of 5 until it gained enough sentience to control the rest of them. Commented Jul 28, 2021 at 17:07

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