Hi Derek - thank you.
When I do a synopsis for a production company, they want everything and of course the ending. And they want more detail in the set up and in the third act than in the second act and they want it written in a compelling way.
It goes like this: if the exec reads the logline you put on the coverage and likes, then he/she will read the synopsis. If they like that, then they'll read the script. So I'd really put your best foot forward when you write that synopsis. It is a skill-set in and of itself, believe me - I write them all the time and it's taken awhile to get pretty good at it.
Interesting curiosity: whenever I read a bad, dull or otherwise just plain not working script? The synopsis, despite my best efforts, also reads poorly. I just can't spin a summary in a better direction than the script was. When I read a really great script, the synopsis is pretty great as well. You're thinking - well, duh - no, it's not that, it's not that it's hard to synopsize a script that is all over the place, because what we do is just truncate it, mentally cut and paste and make it make some kind of sense (it's our job on the line) but it's the inspiration of it. When I read something great, I write the synopsis enthusiastically. So that's why I said earlier - write a GREAT synopsis - make it fun to read. It's your shot, your ticket, your billboard for the script. Draw them in NOW. A boring blow-by-blow will not inspire an exec unless your premise has such a HOOK and is so damn original that they're blown away simply by that. That happens very rarely. Believe me on that one.
That's why I say this:
1) Do tell everything*
2) Focus on the 1st and 3rd acts, with less detail in the 2nd act (but don't leave out the midpoint)
3) Choose colorful, kinetic, inspired language so your synopsis reads entertainingly.
*IMO to leave out the ending will only irk the executive. In a query letter, sure, you're going to be a little coy and only tell them the fundamental premise but make them want to know more. But if an exec asks for a synopsis? Send a synopsis. Synopses aren't teasers. They are summaries.
I read for some A-list production companies and this is my experience with synopses. I'm sure someone will differ so take it for what it's worth.