Plot can be looked at from two perspectives- from that of the reader and that of the author.
From the reader’s perspective plot is the chain you follow through the book, it is the link by link connectivity of the whole thing. It is what affects what, what causes what and why.
The king dies and then the queen dies is a story. The king dies and then the queen dies of grief is a plot. That was EM Forster’s famous distinction. In other words, plot is causal connectivity within a sequence of events. But look closer- the king dies and then the queen dies is still a kind of plot as they are both in the court, the same family, married. It means something- but maybe not as much as the death with a single explanative cause. The king dies and then the plant dies has less common ‘world’ about it- it is closer to nonsense in other words.
Now this is a bit of a side alley we’re going up here but the point is useful and we’ll get back to it later. Now look at this version of plot: the king dies and the queen, who was already feeling poorly, died from the extra grief. In other words a two part, somewhat weakened plot. So plot actually bleeds into world. Where world is what connects everything up.
Now, this talk about world and plot only really becomes crucial when we look at things from the creator’s perspective. The three way relationship between work- audience and creator can never involve all three. In other words you can talk about work and author, audience and work but never author, audience and work at the same time. Something of this realization is behind the enigmatic assertions of Derrida- but for current purposes all we need to know is that trying, as author, to keep your audience and the work in mind at the same time is IMPOSSIBLE. You can flip between relating to the work and imagining an audience responding to it very quickly to simulate connecting all three together but it won’t be a real connection. Far better to separate out the tasks altogether. Think only of the work until it is done. Then imagine you are the audience and then be a critic of that work. Then fix it- again in relating to the work mode. In short as brainstormers know- you are either in critic mode or creative mode- but never both at the same time.
When you are in creative mode plot and world need special consideration. Plot becomes simply: something to write about, something that demands to be written about. Now certain set-ups demand more of the causal twisting and turning kind of writing and others don’t. One size fits all plotting is the death knell of good writing. A fascinating example of this is Robin Cook’s novel Abduction. A sci-fi novel, basically, though written as mainstream commercial fiction, the premise kind of takes off from where the movie Abyss ends. A group of scientists and divers are abducted by an earlier version of humanity living in peace and harmony under the sea. Now the divers have to get back home- and this becomes the ‘plot’. But whoa there. Is that really the most interesting thing we have to say here? I mean, if we really got abducted by super advanced humans who gives a flying burrito for the escape yarn- unless it reveals a ton about what these people are like, their world, and the dilemmas it presents the abductees. In other words, the more unfamiliar the world the more you have to describe that world as part of your plot duty. The more familiar the world- ie. urban new york, the more you can twist and turn in cross and double cross and strict causal linkages as the crime writing master Jeffrey Deaver does. But with Cook’s book when a crime is committed in his undersea world- what he misses is the really interesting bit, which is not who done it or how they are discovered, but the whole nature of the crime, the act itself and how the undersea people react to it. Robin Cook puts up a brave attempt at describing the world he has created but it doesn’t go far enough. He gets sidetracked with his simple escape plot- and in doing so he short changes the pretty interesting premise he has set up.
This, then, is the central function of plot as regards the writer: how to live up to your premise, how to also discover what exactly your premise entails in terms of the plot/world balance.
In general- the more obscure your setting- be it total sci-fi invention, historical, another culture, a foreign country- then you will need more world building and less obvious ‘plotting’, by which I mean a plot structure and plot moves.