The following contains major spoilers for Captain Carter #5, available now from Marvel Comics.
It's safe to say that the Marvel Cinematic Universe has had more hits than misses. This explains why most MCU films now are billion-dollar generators, and why fans are glued to the TV shows on Disney+. However, one big error took place early on in the MCU's teething phase, all thanks to Iron Man 3.
In one of the earliest MCU films, director Shane Black committed what's widely regarded as the cinematic universe's most hated plot twist. It revolved around Trevor Slattery and the Mandarin, angering fans who wanted the classic villain to be shown as a true warlord. Fans eventually moved past the error (largely due to Shang Chi and the Legend of theTen Rings correcting the mistake), but Captain Carter just revived the reviled twist.
Captain Carter #5 (by Jamie McKelvie, Marika Crest, Matt Milla and VC's Clayton Cowles) tells the story of Peggy Carter as she fights to save Britain's soul from the forces of John Falsworth, the Prime Minister who is secretly a vampire. Unfortunately, Peggy was arrested after being framed as an enemy of the state when she unearthed the conspiracy.
John was planning to turn the region into a vampire nation, using Hydra to spread the vampire plague while setting the stage for a global takeover. However, thanks to tech such as the nano-mask and the help of Tony Stark, her allies Lizzie and Harley were able to break her out of jail. However, when Captain Carter confronted John in battle, he confessed that there was no Hydra. It was all a facade he appropriated after Hitler failed to use the group to put his master race into place. The immortal admitted he just needed a distraction so the world would be focused on fighting an invisible army instead of him. He then used the distraction to consolidate power via the Hydra Bill.
Ironically, Aldrich Killian did this in Iron Man 3, using the bumbling actor Trevor to pose as a Mandarin who controlled the Ten Rings. While Tony Stark and his allies were distracted by their terrorist actions, Killian worked in the background to build an army and perfect his Extremis formula.
Even after Killian became a fire-breathing monster, fans hated the film's subversion, despite the masterful acting of Ben Kingsley. Ultimately, the Falsworth legacy pulled off the fake-out much better, deceiving the masses for decades with only Captain Carter able to finally uncover the truth.