No One is Going to "Steal" Your Book Idea
This is one of the dumbest beliefs in the writing community, but it still persists. Ideas cannot be stolen, because if you share an idea for a book, and someone goes off to write 100,000 words that sort of looks like what you talked about, they didn't "steal" it. They wrote a book. You can still write your own take, and get a very different book.

Now, if you wrote the whole manuscript, and someone stole it, that's a different kettle of fish.