Let's see.

You and your friends decided to go on a random adventure. The mountains, you all decided. Though, in the mountains, most of you blacked out. The rest, they couldn't see what was happening. The ones who blacked out, they woke up at the crash site, their memory drained. The ones who couldn't see, they hit their heads on the ice, ending up with the same fate as the ones who blacked out. You all see a little shop nearby. Next to that shop, a small trek will lead you to a village. A small, strange little village, with short houses looking exactly the same. Back to the shop. The shop has supplies and weapons, things to fit your needs. Now, after you get those supplies, you'll have to find clues in order to find out what happened, find the culprits. When does this end? When you want it to, or when the world wants you out. Maybe there'll be suicide. Maybe you'll be knifed through the heart. Anything could happen. Not likely that you'll all survive, but we'll see.
I tried thinking up a legitimate adventure/mystery RP. I think it's better than the ones I thought of in the olden days of BBCode. The rules are the standard rules of Casual. At least a paragraph or two, no powerplaying, etc.