I have been told a Synopsis can be very difficult for most authors to write, myself included. The following information was shared with me from a Acquisitions Editor, so I am sharing it with you.
Synopsis are always written in the present tense. They introduce the
main characters, tell why it is important they be in the story, what
they want to achieve, and what/who is trying to prevent their doing
so, and how, in the end, they overcome the hurdles set in their way by
inner and or outside forces. Synopses outline key elements of your
story, telling facts and events in clear and consecutive order as they
occur from the beginning right through to the end. They do not include
any dialogue. If the story is more complex, you could tell me what's
happening to characters A & B, then begin another paragraph with:
Meanwhile, characters C & D are doing, seeing, learning, hearing...
Secondary characters need not be introduced unless their presence is
vital to the plot foundation. They can be glossed over with such
phrases as "friends encourage/discourage" one or more of the main
characters to/from taking a particular course of action, but...
Holding back surprises of any nature for any reason is not the way to
go. As I explain to all authors who want to withhold key elements in
an attempt to intrigue me, their acquiring editor, I'm not in the same
category as a customer in a bookstore, to teased and tempted into
buying your book. Nor are you a reviewer, who needs to be careful not
to toss out any "spoilers". I require *all* the pertinent information,
including any shocking, surprising, and unexpected twists Please be
assured, this vital plot information will never be revealed to anyone
else if your book is contracted and even more importantly, if it is
not, but it is something I need to have in order to make a fully
informed decision. A full, complete synopsis allows me to seek out
plot holes you might be unaware of in that you're close to the
material and don't see it at once step removed.
I hope this helps.