For some context, I'm considering doing a story with a so called "surprise twist protagonist." I won't go into much details to avoid being self promotional, but the bare basic synopsis is that a pair of sisters and their young step brother have disappeared together under inexplicable circumstances. Their family have hired a private detective to go find them. The location that the siblings have disappeared from is very dangerous, and the private investigator in return has enlisted a mysterious and secretive mercenary for protection while on the case. Unknown to the investigator, the mercenary he hired has an agenda of his own. The twist I'm planning is that the mercenary is actually the estranged stepbrother of the missing sisters and the biobrother of their younger stepbrother. Several years prior, he had committed a heinous crime against his family. For that crime, he was cast out of the family, and made a fugitive of the law. After burning so many bridges and wanting to put his military skills to use, he had taken up mercenary work. When he heard of his younger siblings’ disappearances, he wanted to find and rescue them, but knew too well of the consequences of returning back to their family. Thus, he approached the detective as a hired gun, while taking measures to keep his identity under wraps. To conceal his true nature, the mercenary took up a code name as a pseudonym, presented himself as a mute man who can only communicate in sign language and hand signals, and made sure he never went unmasked around his unknowing family and the private detective employing him. How would you foreshadow a "true identity" twist involving the primary PoV character? Could that be workable in a narrative like I've described? If not, what are the problems with such a plot device?
In my honest opinion pulling off what you want sounds so tough I don't think it's worth it, but I've been wrong before. I've tried to come up with as many different ways to make this work (and stay true to your vision) as possible. At the end of the day I think it comes down to how much narration/perspective you're giving this guy, here less is more. You can do Third Person Limited, and just not say much about his deeper thoughts. Like if he walks away from a Family member because he doesn't want to expose the truth, just say something like "He heard her, but dare not speak, he simply walked away" Also to foreshadow, I would set up a theme early on of "Mercenaries keep secrets" like your detective character hires him so say something like "The Detective hired a mute mercenary, like all Mercenaries he was highly skilled in combat and even more skilled in keeping secrets, and a mute is better than most at that. The Detective didn't know about his past and he didn't want to, he was being paid for his ability to keep secrets, it was no problem if he had his own." Having said all that I still don't know if it would work, because no matter what it is still a main character ripping off his mask at the end saying "Ta-Da I was your long lost brother this whole time" No matter how you set that up, some people are going to say "huh?" So try your best and good luck.
Would it work in a film or video game setting? I was picturing something like a first person perspective game (or even what was done with the main character of the movie Hardcore Henry), were the protagonist is a faceless and silent entity. In my head, his detective employer is ambushed and killed by some kind of antagonist, and the mercenary still continues pushing through the search. What I was thinking is that the mercenary protagonist is visibly very invested in finding the missing relatives, and clearly acts more involved then what a hired gun on a paycheck would. I don't have a coherent vision of how the reveal occurs, but tentatively it will most likely happen when he is reunited with his brother and stepsisters. What might occur is that the siblings might pick on traits they find familiar with the mercenary, like hearing him groan, grunt, etc. in a similar voice to their long lost brother. Either they might pressure him into unmasking himself or take it off for him when he's injured. However, video games are obviously very different mediums then novels. What works in one context will necessarily not work with the other. A first person perspective likely isn't going to translate well into text dependent written works of literature.
Execution will require a lot of forethought. Best to cut down on the contrivances, or mask them well with simple solutions. There's nothing wrong with the POV hiding something from the reader—unreliable doesn't have to mean insane—but the way he overtly hides every aspect of his identity in a somewhat blunt way calls for plenty suspicion. I would soften that end. Maybe he gained weight, grew a beard, cultivated a mullet, donned sunglasses or coloured contacts. Maybe his years as John Mullens really have changed his general demeanor so as to be hardly recognizable. Does the reveal need to be a Scooby unmasking (nothing wrong with that), or could it be a moment of weakness/need/tongue-slip, where he simply says or does something that immediately tells them his identity? As for foreshadowing I think the fact that he goes above and beyond a merc's commitment is pretty good. It could also just be small things, like knowing where a key is hidden, or a particular habit of another character: "How did you know you'd find me here?" ...basically things that can plausibly wear the mask of gumshoe intuition but seem like bright signposts after the reveal.
