Many are asking how 343i will dig themselves out of the hole Halo 5 left the story in. So many theories, and so many questions about whether they’ve changed the story or not. But try following through my theory and predictions of how the parts of the Reclaimer Saga plot fit together and reveal Cortana’s innocence…
THE HIDDEN MYSTERY SET-UP.
Alongside Halo 5, 343i launched The Fall Of Reach animated movie. In it, Master Chief asks Blue Team “Will you trust me? Will you follow me?” into Halo 5.
Why? Well, we were given two points of view to believe in Halo 5. But did you trust “new kid on the block” Locke’s point of view with his “Cortana is behind the Guardians, as per Dr. Halsey’s theory”? Or will you trust and follow Chief and his viewpoint from his experience in Halo 4? “Who is right? Locke or Chief?” (XBox Halo 5 website, original advert questions). Let’s see which path to choose through Halo 4, 5 and Infinite’s plot.
(1) Halo 5’s “The Cost” trailer: Chief asks us "This [we see Chief’s point of view through Chief’s visor]. Is this what you [the player] wanted? Is this what you were looking for [Chief’s point of view]?".
Well, have they changed the story? Let’s see what 343i’s Pictionary style “Hunt the truth” Story in the Halo Infinite “Become” trailer reveals:
(2) Now watch the times below in “Step Inside - Become [Master Chief]”, to see Chief’s point of view about Halo 5.
(a) Time 1.17: Seeing through Chief’s visor, we can now “re-boot” the Halo 5 story, as we’re asked “Initialise?” Click “Yes!” to start looking at Halo 5 again, same story, but from a different point of view - Chief’s!
(b) 1.29: with “older, wiser eyes” that are “looking for what is right (to their right)”, we “look ahead” to Halo Infinite, but in seeing Chief on a circle putting his armour on, we’re also see a “reverse” or mirror picture of Chief taking his armour off at the end of Halo 4.
(c) 1.30: remembering “knowledge is power”, something will finally “click” into place for you…
(d) 1.31: Then your little “face will light up” with the light that is “gold / buried treasure”, having now “FOUND the truth!” - when you BECOME Master Chief in Halo 5, and see the story from Chief’s point of view. But what was it?
(e) 1.42: Chief’s viewpoint in Halo 5 revealed! But will you trust Chief and follow him? For we now come full-circle (round space station), back to where “high above the planet” like the end of Halo 4, where we heard these piano tones before (sure your inner Master Chief is ready to “get back in touch with his feelings and humanity?”), because from Chief’s point of view, the end of Halo 4 was when Chief thought “R.I.P. Cortana, another fallen Hero of Reach” because “I… watched… her… DIE!”.
So, in Halo 5, if instead of Locke, you now trust what Master Chief believes he saw happen, then we must ask “If Cortana is dead - including ALL her fragments - how could that be Cortana behind the Guardians in Halo 5?” Cortana must be innocent, and the supposed “Cortana” in the Cryptum must be an imposter set up by a hidden enemy as part of a sinister plot. Then we also don’t have to “work out ‘how Cortana turned evil’”, but only need to ask “Where is this AI getting her information about Cortana from to do this [poor] impersonation of her?” Oh, and “Who is the hidden enemy she serves?” Since it’s about reclaiming the Forerunner superweapons, surely, as Master Chief, your first suspect would probably be the Didact…
DISCOVER HOPE IN HALO INFINITE.
In trusting Chief, we also have to wonder what kind of “death” Cortana died. Was a death like Sgt. Johnson or Miranda Keyes? Or was it a “Memories of Reach” death - you know, where around the age of six or seven, Spartan II’s like seven year old Cortana “appeared to die”, but in reality, they’d been “abducted and replaced with an identical clone”?
One means Cortana is gone forever, but the other means she could still be out there, waiting to be found in “the greatest hunt in gaming history”…
So, having uncovered the truth about the imposter in Halo 5, we can now ask that as Chief’s famous “luck” would have it, did Chief get the answer about the imposter right, but for the wrong reason?
For when the chips are down, and we’re wondering how we’re going to defeat the hidden enemy of Halo 5, the fake Cortana’s hacked AI Army and the Banished, then perhaps “as Chief’s luck would have it”, as we look up for hope into the starry night sky of Zeta Halo, we finally see the remains of the Didact’s ship from the end of Halo 4 - still carrying the last surviving fragment of the real Cortana onboard - as it finally crash lands on Zeta Halo, so that the real Cortana returns to help Chief “Finish the fight” in Halo Infinite, looking something like this?
BACK TO THE HUNT.
So, there it is: if true, the keys to unlock the Mystery Story in Halo 5 are “Chief’s point of view”, with his “Memories of Cortana” and his “Memories of Reach”…
But if now know where to start by investigating the imposter “Cortana” for any mistakes she makes in impersonating Cortana, can we finish solving the “Hunt The Truth” Mystery Story in Halo 5, and find out:
(a) if the AI’s were tricked into an “AI revolution”, or hacked and being remotely controllled for use as Cyberweapons?
(b) help Chief uncover the hidden enemy behimd the Guardians as we travel to investigate the suspects from:
- Kamchatka (a plot by the Didact?).
- Argent Moon (ONI’s Argent Moon Plan, because they’re certainly trying to cover something up in Halo 5?).
- Meridian (Insurrectionists?).
- Sanghelios (a Covenant faction?).
- Genesis (Forerunner again, as if to double-check “Are you sure it isn’t the Didact behind it all?”).
This could keep us busy as we wait for the climax of “the greatest hunt in gaming history”, when Halo Infinite finally, slowly, reveals “the truth” for which we were hunting all along…
After all, as the new trailer asks, was Cortana framed with “the hallucinations of an aging Spartan and his malfunctioning AI”, or was it more just "Did you hit your head or something?".
After all, “Don’t you remember?” Captain Del Rio’s Orders in Halo 4?
So whilst The Weapon’s purpose is supposedly “to help clean up this mess” by “getting Cortana back into the chip”, it’s Chief who’s still supposed to obey Captain Del Rio’s orders from Halo 4 and take Cortana back to the Infinity for final DELETION.
And if that happens, ONI can finally bury the truth permanently, and by blaming Chief for disobeying Del Rio and running off with Cortana in Halo 4, Chief and Cortana will carry the blame for Halo 5 forever!
Now, like Master Chief, we’re not just going to stand by and let that happen, are we? Even if it does means going a little “rogue” like Chief… 
Hey, at the very least, even if this isn’t the story 343 are following in Halo Infinite, it tells you how I’d have written it, and, well, it’s at least a good theory, isn’t it? That the real Cortana is innocent, and when Chief reclaims her like he did from High Charity in Halo 3, they’ll reunite to finish the fight in Halo Infinite, even as Chief faces what happened to him and the Spartan-II’s as a child, so reclaims his humanity from his past to become the human Reclaimer of his future.… 
“For the seeds of our future are sown in his past” (Arbiter, H5 trailer E3 2014).