Hey! I finished my first MS a few months ago and it's being beta-read now. I know that I'm not quite there yet, but I have started thinking about the outline of my query letter and I'm already stuck. Especially in this genre, where world-building is paramount, how much of the query letter focuses on telling the agent what the world is about vs. the plot?
I don't want to give my actual plot away, so an example of what I'm talking about is below:
An alien race conquers Earth and enslaves mankind. Obviously that would shape all of society on a very fundamental level, driving main character motivation and overall growth. While this plays in the background, there is a central story, say "boy meets girl" that has the potential to actually change the status quo of aliens enslaving mankind.
So, do you just introduce the world in the first sentence and then tell the "boy meets girl" plot in the rest of the query letter? Do you just balance as best you can?
Does this make sense?
It really depends. How critical are particular world building elements to the plot? It gave me fits writing the query for my (ultimately unsuccessful) first novel, because certain elements of the magic system really did drive the characters goals and obstacles.
World building does matter in speculative fiction, which makes it rather challenging to query compared to other genres (imo). There is such a range of possible settings, time frames, and historical periods to draw from, not to mention the possibility of worlds made up from scratch. You could have the same basic plot (say a retelling of Romeo and Juliette) set in an endless assortment of settings, historical periods, and world types. Readers have setting and world preferences in SFF. Agents have definite preferences too.
So I think it is important to get some hints out, at least, about the kind of world your story takes place in. But the challenge lies in not drowning the thing in extraneous details or in jargon or terminology that is confusing without explanations or the kind of revelation that comes from reading the story.
As for giving the plot away, you have to do this when querying a novel. No way around it. Agents won't buy a pig in a poke (as the old saying goes), and your fellow writers can't help you without your sharing your work with them. In the tradiitonal query letter, you generally include the plot set up to the point of revealing the stakes or major decision the protagonist has to make. It's similar to a back cover blurb in that it doesn't tell the reader the ending of the story. In the synopsis, however (which is not always requested), you do have to include how the story ends too.
In addition to what lizmonster said, a synopsis is not always required, and when it is, not always at the same time as the query letter.
In my experience, agents in the US tend to request synopses (if they do at all) if they ask for more material after an initial query. It's been a couple years now, but I don't recall any I queried wanting a synopsis at the same time as a query letter and any opening pages.
Unfortunately, different agents have different length requirements for synopses when they do request them. Some writers have 500, 100 and 2500 word versions of their synopsis on hand.