It's rather tricky because nowadays the words summary and synopsis are interchangeble, but while one means to quickly give a brief description of the entirety of the story, one is simply a brief hook. I gather you're trying to get the "brief hook" yeah? It's essentially just mentioning all of the details that a person can easily understand as things they should care about when they start reading the book. It's almost like a small primer of the main thrust of the story's plot, I can use Blast Back as an example, actually...
Actually I'm going more for the quick explanation. ^^; I figure I have the brief hook, but perhaps I'll let you (and anyone else who wishes to contribute) be the judge of that:
When fifteen-year-old Gwenyth Lamelle comes across nine artifacts her father brings home one night, she accidentally releases the powers locked within them. Now it is up to her and her two mysterious guardians to reclaim those lost powers—before they fall into the wrong hands. In a world ruled by gods, spirits, demons, and other mystical beings, the trio are in a race against time, with the fate of the world—of all worlds—hanging in the balance...
I know. It needs work. >.<
It's essentially what you get a guy doing trailer voice overs to say, right? This tells us what we have to look forward to, but without spoiling anything that we don't really learn early on. Might help to build a list of the key plot points, then cut it off at the point where the main character(s) come to a decision of what to do, noticing what is ahead of them. Then of course, cut out some of the plot points that aren't quite as necessary if needed.
Thanks, TxA. ^^ This helps a lot. Once I get it done, would it be alright if I asked for your input? ._.