You would be amazed at the amount of times I come across a synopsis that is simply a summary of a book’s narrative (well twice so far this week but I am not really counting).
A writer must remember that a synopsis is a sales document. Its job is to convince the publisher/agent that the book in question is a commercially viable project. An outline of the book’s story IS important but please keep it brief. Instead focus on explaining where your book will fit in the market, who is likely to buy your book and what you can offer as a package.
IF the publisher/agent thinks your book is interesting, they will read the enclosed extract and then (hopefully) ask for the full manuscript.