hidden book

My scrivener tutor package has suddenly replaced my book. I am not remotely computer savvy, and no action has provoked this calamity. Please help!

Are you talking about what is currently open? You can have hundreds of projects on your computer (the tutorial being one of them) and as many as your computer can handle—just like you can open five .docx files in Word. So if you closed your project and loaded the tutorial, I guess you could define that as “replacing” the original, but all you have to do is open the work in progress project. Maybe see if it is in the File/Recent Projects/ sub-menu?