The "From Dusk Till Dawn" Effect

(this could, I suppose, also be called the "Psycho" Effect)

(inevitably, spoiler alert)

When I was in my teens I watched From Dusk Till Dawn with my mum and dad. We put the video on reasonably late in the evening; by-and-by the film advanced as far as Clooney and Tarantino crossing the border and arriving at the Titty Twister. It was at this point, as it was late, that I went to bed. I hadn't seen the film before, but knew (roughly) what it was about.

What I did not know was that my parents knew nothing about the film. Nothing at all. My nan had cable TV and we did not, and she taped films indiscriminately, giving us a dozen films a month to watch (and then return, she liked to collect them). All my parents knew, at the point that I went to bed, was that Clooney and Tarantino were ruthless criminals, not averse to murder, kidnapping, robbery etc, and that they had arrived at a bar in the Mexican desert. They knew nothing of the plot that was to unfold from that point.

You can imagine their shock (and what they said to me the next day, as it had been my suggestion originally that we watch it).

I was musing on this today, and wondering about how this kind of shock might be put into a role-playing game. I'm not talking about a game of Cyberpunk where a bank job suddenly goes wrong: while you might have hoped that it would go well, it's not inconceivable that it would go wrong. I'm not talking about a game of D&D, where the sorcerer says, "I am your father."

My thought is about genuinely surprising players:

• vampires suddenly showing up in a bar, in a world which to all intents and purposes is completely normal;
• a player taking a shower, suddenly and brutally murdered, after successfully rolling persuade and evade so many times talking to cops and used-car salesmen, travelling across country with ill-gotten loot;
• a group of players suddenly discovering that one of their own has been the secret villain all along, a la Keyser Soze.

Being relatively new to the hobby, I don't know if there are any games that have similar mechanics; I don't know what would work well. I guess the key concerns - as a GM - would be knowing that your players could handle such a huge shift ("the game is no longer about hustling and stealing, it's about getting out of the city before the alien hunter killers find you"), and about setting up game mechanics - and player/character mechanics - that would realistically cover both genres seamlessly.

I have no idea if this would work - and having posted it online, I don't know if any future players might suspect I was going to do it if I got the chance to run a longer campaign. I just have this idea that if it was presented well it could provide a huge but satisfying narrative twist to a campaign.

Enough of me though: anyone out there got any thoughts/comments/ideas?