Avengers: Endgame featured a lot of references to the comics. One such nod saw Captain America take possession of Loki's scepter from HYDRA agents that had infiltrated S.H.I.E.L.D. In order to trick them into thinking he was on their side, he said, "Hail HYDRA." This line was a reference to the controversial 2017 Marvel event Secret Empire in which Kobik -- a sentient cosmic cube -- rewrote history to make Captain America a HYDRA sleeper agent. A theory on Reddit speculates the moment could set up a Marvel Cinematic Universe adaptation of Secret Empire.

According to the theory, Captain America using Loki's scepter, which has the Mind Stone in it, to defeat his past self would likely have been mind-scrambled and susceptible to the influence of others, particularly the HYDRA agents coming off the elevator and under the impression the hero was secretly one of theirs. The theory then says the HYDRA agents could take that Captain America for a debrief, with the seeming confusion resulting in a vulnerable Steve believing himself to actually be one of them.

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While that would seem to be a drastic turn for the now retired hero, the theory is quick to point out that the timeline the Cap vs. Cap fight takes place in is the same alternate timeline in which Loki escaped with the Space Stone. With his own Disney+ miniseries forthcoming, Loki is expected to appear in the alternate timeline where the continuity is less complex and the stakes aren't quite as high, at least as far as we know right now.

In Loki, and the related What If... series also planned for Disney+, the possibilities for what can be done in the MCU multiverse are endless and a story where HYDRA has its very own Captain America is an intriguing possibility. Coming at a vulnerable point in MCU history between the battle of New York and the exposure of HYDRA in Captain America: Winter Soldier, the terrorist organization recruiting the Sentinel of Liberty could have massive consequences.

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When the story started in the comics, many found the move unsettling. Even before the story arc really played out and any avenues were explored for just how Steve had secretly been a HYDRA agent for so many years, the arc was criticized for turning a longstanding beloved character representative of America into a Nazi. Particularly because the character's original creators were Jewish, and the image of him punching Hitler is so iconic.

Of course, nothing in comics is permanent and the controversy eventually died out. Reality-altering shenanigans turned out to be at play all along and the real Captain America was as dead set against HYDRA (and Nazis) as ever. Adapting the story to the MCU, but doing so in a setting that's explicitly alternate reality from the get go may be an easy way to drum up publicity and intrigue without the backlash the original story drew.

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There are definitely a few problems with this theory, though. The Mind Stone's powers are pretty varied, and it might not even work in the way the theory describes, or at least for long. There's also the question as to whether the HYDRA agents would actually take Captain America way and de-brief him if they already think he's one of them.

All in all, it would make for an interesting storyline drastically different from anything done before. While Chris Evans himself is unlikely to return to the roll, obscuring an actor's face with his mask or using CGI would both be viable options for making the element work, as the theory notes. There's no doubt that the Loki series and What If... will go down some wild routes, and as far as the possibilities go for alternate dimensions this one seems pretty tame.

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