A query and a synopsis are two very different things and should not be replaced for one another.
Query: pitch including your hook, brief overview of the book in a captivating blurb, and short bio including your writing background and distinctions.
Synopsis: a summary of your work outlining all the plot points and major characters.
A synopsis should never be sent in place of a query. A synopsis typically does not make an agent want to request more. Your query should be enticing and intriguing, and a synopsis is straightforward and factual. You don’t want to be mixing these up or thinking a synopsis is a suitable substitute. A synopsis is useful in its own way once an agent does show interest.
Additionally, do not plunk a long synopsis into the middle paragraph of your query letter. Tailor it to be an enchanting overview paragraph that leaves the reader on edge.
I know it’s hard to take a step back and be objective of your work. Many writers think that their synopsis is important to show an agent the true strength of their book and its nuances, but I assure you that part of being a writer in today’s publishing landscape is knowing how to pitch yourself. And a query letter is the first step.
Learn query letter basics here.