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Compile a brief fact sheet about the book that details the title, author, publishing house, word count, a summary of the book and also character sketches centric to the main characters and any other "speaking" roles in the book.
This information should be shared with a director (if you are working with one), prospective narrators and will also come in handy when promoting your audiobook.
A document such as this should be concise and give the reader immediate insight pertinent to their potential involvement or commitment to the audiobook. If characters are few, your discovery document should run no longer than 1 page or 250 to 500 words.