I got this question recently:
“I love to have a twisted ending. I want the reader/audience to sit at the end of the movie/screenplay with mouth on the floor, and say, Oh, that was a badass ending. What is the best way to include this in the query letter without making it a dead give away? Or do you want it to be a dead give away?”
I’ve gotten this question a few times. I don’t think there is a right answer to this question. The main thing you want to do, at all costs, is get people to read your script, so if that means giving away the ending in your query letter then that’s what you have to do. If you can write a compelling query letter without giving away the ending, then great, but if by giving away the ending you feel like your query letter is better and you will get more requests for the full script, then that’s what you must do.
I believe you tell the story — beginning, middle and end. You aren’t trying to get someone to come to your movie with the query letter, you’re trying to get them to purchase the script and invest millions of dollars in a film. Knowing it has a “killer” ending would make them more interested, not less.
I agree with your sentiment… you want them to request the script. My main reason for constantly telling people that they need to demonstrate a beginning, middle and end in the synopsis is because this demonstrates (hopefully) that you screenplay is well structured, which is a key ingredient in getting a producer to request it.