My main character has a "secret" that is slowly revealed to her love interest throughout the first half of the book. I would never reveal this secret on the back of the book cover, but I have reveled the secret in the query. The discovery of the secret is a pivotal plot point and my understanding is that agents prefer that you tell them what the book is about without a lot of innuendo or mystery (but obviously with a good hook and great writing!).
Revealing the secret has caused a problem for a number of my critique partners, who then spend the first half of the book commenting, "I know XYZ. Why do you only allude to it?"
I have been assuming that agents will separate what they know based on the query from how the book will read to someone who picks it up in a bookstore.
So this is my long winded way of asking: Should I reveal the secret in the query?
If you won't put it on the back of the book jacket, don't put it in the query.
I like to read queries and pages as though I am a reader in a bookstore. Surprise me!
Of course, you have to entice me to read the entire novel in the query so you need the good hook and great writing, but you don't need to reveal the secret in the query.
Also secret should not be in quotes. Putting quotes around something means it's not what you're calling it.
Example: writing Janet is "nice" means you know Janet isn't.
Misuse of quotes is often pretty funny as in chalkboards outside grocery stores advertising "fresh" veg, or "tasty" cookies.
It's not funny in queries.
If you're not sure about proper use of quotes, don't kick yourself. We all learn by doing. Get a copy of Eats, Shoots, and Leaves by Lynne Truss and learn through laughter.