[BetterRed]

@C-novice - have you checked the Trash?

If you have you turned off the Remove book confirmation message you may have inadvertently deleted the book - happens quite often. Coming from Windows you might expect a confirm message because it's message is not dismiss-able, that said the confirm delete can be dismissed in Calibre on Windows.

An extra click or keystroke occasionally is a lot less bothersome that having nagging doubts about the software when something goes missing, especially if one doesn't keep the originals like you do, or take regular backups as many don't, or if like me, you empty the Trash regularly.

BR