It's very easy to write a story for an event. It's vastly harder to write plot. It's even less likely to write plot that makes sense after the players get to it, and you'll need to have some mechanics to enable the players to make an utter mess of the plot you've carefully created for them.
At the start of an event the players have a situation. They have a reason to be where they are, and some stuff they know about how they got there. For Dark Hearts the players were Heros who had answered the Empires call and gone to save resources/villagers from an approaching orc force. For Alone often the players were an engineering crew or soldiers who were being sent to a suspect location by some corporation. For Slender events we're paranormal investigators going to somewhere where paranormal activity has been reported. With a 'Saw' themed event you might wake up in a small room with no idea how you got there and possibly minimal information about who you are.
I like to start my events with very little background. I know why I believe I'm there, and I know what I think I'm trying to do, but usually this is the extent of my knowledge (other than how my char fits in with the wider world). We do get players who want more. I can understand that that's their style of play, but given the way we write games and the way I think about the games I'm writing it's hard to work out what extra information our players are after. Briefings are given in game, often by the commanders the players have picked themselves, or packs are handed over at the pub in the hours before time in, and the players are dropped in running.
I tend to find people who run events have patterns they tend to follow regarding pacing. Some of this is dictated by timings they run to, but event those are often chosen and stuck to by organisers. For example, at Mandala 24 hour time in means 24 hour things happening at all hours and if we think too many people are sleeping we'll find ways to wake some of them up. At other games often much less happens from 2-3am until 10am. We benefit from having refs who are early risers and others who sleep late. We have shift systems for monsters to ensure people are awake through the night and time out between midnight and 3 on the sunday morning to give people a chance to sleep.
We also like to time out at a dramatic moment. We will build up to a shuttle launch, or final large battle and rarely play through the effects of it for long. Players can make that bit happen without us.
We've had to ban individual 'thank you' speeches. Too many people were getting missed because having run on almost no sleep for the last few days and built up to running around with flares in the dark to make that ending special for the players is not conducive to remembering who you have to thank. People always get missed and they're inevitably tired enough that it's not as easy to ignore as it should be.
Events normally involve things happening for us. These can be the result of things we do, the result of things the players do or things that are entirely unexpected and no one ever works out quite how they happened. Usually there are things that players can't stop. Some of these are things that've happened before the players got there. We like to give players choices and have things that happen as a result of the choices the players make. If the players feel they were responsible for the choice they're more likely to feel personal responsibility for the effects of that choice.
We aim to give the appearance of choice. We cannot guarantee what the players will do, and we aim to have options for as many of their actions as we can predict. You can often give the illusion that the players actions are having an effect whereas both of the two most likely choices had the same outcome. We will ignore entire sections of game if the players don't take the hook even if it means they don't get to see a lovingly prepared set piece. The set piece doesn't add value if it's forced in to a plot where it doesn't belong. There have to be coherent reasons for each happening even if the players can't work out what they are.
We have people who spend most of their time at our events writing and rewriting plot to respond to the players actions. Finding out what the players are planning and working out how we respond to things are major uses of our resources. We've had one game where the plot was being rewritten constantly and had five major rewrites with new endings and new story lines over the course of the weekend. They did end up with an ending very similar to the one we'd originally written, but that was by no means a sure thing and they took an entirely different route than planned to get there. For that event we had a few people comment to us that the plot had seemed a bit linear.