Need practical help for turning a story idea into a story for a game

[Anian]

OK, I don't really know how I'm gonna handle this, but here we go. Little background to why I'm doing this: I have this plethora of ideas for cyberpunky story, but I wanted to get my beak wet first, so before Halloween I decided to make a vampire game (think "A Vampyre Story" type of thing, in fact a lot like it in tone at least). Well of course I won't finish this before Halloween, among other things because I can't really round up a story the way I wanted it, even though I've been thinking about it for a week or so. But I still want to do it.
It should be a short (like MAGS/first time) game, 10 rooms tops.
I'm asking for help and opinions, plus it might be a good exercise/tutorial that other people might find helpful (how to develop your story beyond initial idea and adapt it to an adventure game, that sort of thing) and that's also why my thought was to I put it in the Critics' Lounge and not Recruitment or Adventure talk. Not really expecting for somebody else to write a story for me, just pointers and helpful advice and critique. It's more about writing than this specific story.

What would be the basics:
We find out about how Maximillian (Max) became a vampire from an intro that goes on inside a coffin. Cutscene would be with finger/hand puppets (drawn). Shorter version: a prince Max was happily in love with a princess, until a Stranger came into the land  and charmed the princess with stories of heroism etc. Max decides to kill a monster in the haunted castle that's plaguing the land and of course it turns out it's that Stranger and he is a vampire. He bites Max and shuts him into a coffin and leaves him there to suffer knowing what will happen to the princess.

Max being weak, because he just became a vampire, can't open the locked coffin, but is still "alive" and preforms this intro with puppets that he made out things that were in the coffin. In one of the performances (the one in the intro) is cut off by voices of teenagers, who break the chains (with pliers or something) and open the coffin. Teenagers would be 90s goth kids who were in this basement of the caste, summoning demons etc. (candles and a pentagram on the floor) and trying to look into the coffin.
So apparently centuries have passed since Max was trapped in the coffin and now he wants two things - maybe a snack (but I'd like to keep the goth kids at least as zombies if not alive) and find out what happened to the princess.

Throughout the game Max uses the dolls to hypnotise a guard for example (so there's an established mechanic/option for a solution) and in the end "battle". Turns out that his princess has become a vampire and doesn't really remember Max or has become cold and heartless, so Max will preform the puppet show for her which will make her cry/remember and boom happy ghoulish ending.
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What I'd like is some ideas for the middle part (and I know it's a big part, but that's kind of the point for learning). Game starts of in a castle, so I thought maybe the castle is being demolished or something and princess is behind (she became and exec of a big corporation or something), but I really can't fit that into a small game somehow...or can I?

Feel free to pm me although I think it'd be nice to have the thought process displayed for other people to learn from it. How to actually form a short game story.

[Babar]

I find it helpful to lay out the game in terms of goals desired to be achieved, and then fit in obstacles to those goals to create the puzzles.

So the end-goal here seems to be "Get the girl".
To get the princess, he needs to:
Gain back some strength.
Find out where the princess is.
Get to the princess.

How will he gain strength?
He can get some blood from the teens.
How will he get blood from the teens? (He's a bit too weak to attack them right now)
He trades them something.
What does he trade? What does a goth teen want?
He gives them his spiffy black collared cape in exchange for some blood.

How does he find out where the princess is?
He asks around. Some people direct him to go to the museum or library.
The library gives the location, but the door is sealed, and the library makes mention of some artifact needed to open the seal is in the museum. Getting into the museum requires purchase of a ticket.
How does he get money to pay for a ticket?
He does his puppet routine on the long line of people waiting bored to get into the museum. Some of them toss him some coins, which he uses to buy a ticket.
Once inside, how does he get the artifact from the display case guarded by a guard and security camera?
He's a vampire, so his image doesn't show up on cameras, and he distracts the guard with a puppet show (again?), and nabs the artifact, and uses it to get into the sealed castle with the princess.
How does he free the princess from the clutches of the monster in the castle?
PUPPET SHOW AGAIN!

You obviously wouldn't be able to use this one, it is far too short and too many of the same puzzle solutions, but perhaps it can give you some ideas. I sort of morphed it off Rodekill's old puzzle tutorial, you can find a version of here (click Tutorails).
Still, I'd say the basic structure would be the same. Take plot-points, convert them into the result of obstacles that have been overcome, and then divide those obstacles into further obstacles. So:

How to gain back strength to travel about?
Get blood from goth kids.
How to get blood from goth kids?
...
How to find where princess is?
Check the local library/museum/professor of history.
How to get to those locations?
...
How to free princess
Also get info on how to from library/museum/professor.
How to get items required to get to princess?
...

And so on. At least that is how I do it .