Zombie Apocalypse Initial (incorrect) Premise (RPG)

[Max_Writer]

I've been wanting to run a BRP modern game that would, during the first game session, devolve into a zombie apocalypse. My problem is, I don't want it to start as a zombie apocalypse game. Rather, I want it to start as "x" game that turns into the former, hopefully shocking the players. However, I can't figure out what the initial premise would be for players to create normal, everyday investigators without giving the real premise of the game away. I've gotten a few ideas online (prison, school, college, supers, film crew, class reunion, Survivor or survival, The Sims) but that still doesn't give me my initial (false) premise, my "This is what the game is going to be about."

I feel like I'm explaining this badly. When you start almost any game, one of the questions is "What kind of game is it?" The answer is fantasy, horror, or the like. I need that initial fake premise that will get the players interested, get them to make normal people as their characters, and leave them completely blind-sided when zombies start showing up when they shouldn't even be in such a game. The premise should be 20th century <what>.

Here's a good example that worked in play. Year of the Phoenix started out with the characters part of a NASA anti-terrorist space force in 1999. Characters were part of the military but trained to pilot shuttles and deal with terrorism in space. However, during the initial scenario, when they take the shuttle Phoenix to the international space station, which has been taken by terrorists, the space station explodes as they close to dock. Everything goes black. They wake up on the shore and guess that they managed to get out of the shuttle. Turns out they are probably in the Soviet Union (which still existed in the game) and help some rebels fight against them. However, by the end of the mission, they find that they are actually in the 24th century and the Soviet Union now runs the world.

Any advice or ideas are welcome. Thanks.