So, I'm working on a story where the plot is roughly this: A group of high schoolers are on a camping trip on Halloween with their teacher, and as part of a spooky story they take part in an old folk tale ritual of placing stones marked with blood into a fire. If any stones were missing by morning it is said that the owner would die before the following Halloween. Every stone is missing aside from two, one of which belongs to my main character (this is revealed at the end to avoid lack of tension). The next year the children are either tricked or are trapped by events outside their control in the school the night of Halloween. The teacher turns out to be an ancient being (probably a witch) that feeds once every 100 years on the young. They are stalked and killed one by one and have to fight back against something far too powerful that seems to know their every move. It'll be pulpy and fast paced, so I want the premise to be as straightforward and believable as possible. My problem is, I can't decide how they should be made to stay at the school that would be believable. I'd like it to be dramatic like a snow-in or extreme weather (it's set in Wales) but snow doesn't make much sense in October unless it's the Witch's doing. The other idea was to have the teacher have a Halloween themed midnight party held in school that only her favourite class is invited too, but this seems rather too mundane (possibly just me being too critical) Are there any other ways that you can think of to trap a specific group of kids in a school overnight on Halloween with their monstrous and murderous teacher? Help!