The PCs are all Apprentices in their various fields. One day, it is discovered that their village/town/etc is under some form of iminent threat (advancing horde, dragon seen nearby, James gang riding in, whatever). The town leaders get together, and decide that someone needs to go get help from regional authority (the duke, the marshal, you get the picture). They don't want to send any members of the local constabulary since they will be needed to keep the peace/defend the village, so they ask the Masters to send their best Apprentices to ride for help. The logic being that the best students can be trusted with the job as well as being competent to do it.
The fun comes in when the players decide if that's true. Maybe they are the Master's best pupil. But maybe, they are the worst, and the Master wanted them far away so they didn't mess up the defense of the village. Or maybe they have a relationship with the Master beyond what simply teacher-student. It could be romantic (either condoned or illicit), or it could be familial. Whatever it is, the Master sends the PC for help to get them out of the village and out of danger.
Hopefully, the party will at least have enough top grade students to fullfil their duty (and survive), but it's the other students that will make the job interesting.
I have never LARPed, personally, but the ideas presented here are very compelling. They could be easily adapted to other situations, such as running a haunted house during Halloween, and some of the ideas (the sounds and smells, especially) can be easily incorporated into tabletop sessions. Thanks for the ideas.