I'm currently querying my novel and have discovered that many agents seem to want a synopsis as well as a query. So I read up on how to write synopses, and it appears a synopsis of a novel tells the whole story, beginning to end.
My book has a major plot twist toward the end, and revealing this in the synopsis seems like a really good way to make sure the agent won't bother reading the MS.
Do I really have to give away this major piece of plot in my synopsis?
I'm afraid so.
Agents and publishers use synopses to make sure your novel has clear story and character arcs, a plot that hangs together and makes sense, and a plausible ending.
I know it's tempting to hold back something as important as a major plot twist, but by doing that, you're actually weakening your synopsis by not showing the agent reading how genius your plotting or character development really is.
Just make sure you seed hints to this twist through your synopsis the same way you no doubt have through the novel. I've read synopses for novels with big character reveals or twists in them where they appear, in the synopsis, not to make any logical sense because the seeds haven't been planted earlier in the synopsis. And these were for books I'd read and knew the author had very cleverly pointed toward the twists throughout the book without making it obvious that's what they were doing.
It makes writing your synopsis harder, but yes, you do have to reveal that twist in your synopsis.
Hope that helps!