|Cram, cram, cram. It will fit.|
1. Whose story is this? What is the story?
2. What is your inciting incident?
3. What is your climax?
4. What are the major events that got us from the inciting incident to the climax?
You will need #1, #2 and #4 for writing your query. Maybe #3, maybe not. The goal of a query letter is to intrigue the reader enough to want to see more. To do that, you need to write something that communicates the following:
This is an INTERESTING CHARACTER (see #1) with a SERIOUS PROBLEM (#1 and #2) that he or she is DOING SOMETHING ABOUT despite the danger (#4)
Apply Occam's Razor liberally. Ignore the blood for now. Don't worry about voice, even, just get this on the page. Various sources have pointed out that the above information will probably cover about the first third of your novel -- which is true because in the first third we meet your characters, get through the inciting incident, and make some progress toward the goal despite dangers and set-backs.
Then give the BOOK'S NAME, WORD COUNT, GENRE, and list any publishing credits you may have, awards you WON (nobody cares how close you got if you didn't win), and/or prestigious writing programs you've graduated from.
Then thank the reader for their time and sign your name.
Bam, done. Now put it away for an absolute minimum of 24 hours and get something done on your current project -- because you've got something new in the works, yes?
When you come back to your query, re-write it to add voice if you can. You'll probably notice other problems. And once you've made it as clear as you can, you're going to need to show it to your fellow Writing Hell sufferers. Preferably ones who know nothing about your story. They will explain how you have failed to do any of the things listed above even though you really tried to.
That's okay. Revise and repeat. Going through six or eight drafts is not unusual and does not mean you suck.
You will question the clarity of your story at some point, though, and that is not a bad thing. Maybe a little trimming in some places, expansion in others, would make it easier to answer question #1 above. Maybe some scenes need more focus so it's clear how they fit into question #4. Did the inciting incident (for #2) need to be more dramatic? More traumatic?
These are all vague questions, I know, and only you and your gut can answer them. Writing a query during the revision process helps me think about them, I've found.