In high school some friends and I discovered what you might call an advanced sex ed book, stashed in the school library. It was thin and softcover, like a workbook, and had lots of graphic ink-wash illustrations of naked women and sexual positions. We spent a lunch period giggling over it and then re-hid it inside a larger book we figured no one would ever open, a Native American history book.
A few days later I returned alone to the library with the intention of smuggling out this book. This was before the advent of easily-available pornography on the internet, and while all things considered the book was probably pretty tame, by my sheltered 15-year-old virgin standards it was plenty titillating. Wank material was difficult enough to come by that I figured it was worth the (what I thought to be) minimal risk.
I got down the history book and, when no one was looking, covertly transferred the sex book to my backpack. Then I sat at a table pretending to read something while I gathered my nerve to head for the exit. As far as I knew, with the book safely hidden in my backpack I was scott-free... but there was something nagging at my subconscious, something that told me I shouldn't try leaving the library with that book. I had no idea what the problem was, only that I was sweating and nervous and all but physically rooted to the spot.
Just as I was about to force myself to go through with it, I suddenly noticed a woman standing on the other side of the room, facing and seemingly staring right at me. She was tall and had long curly blond hair and pale eyes; in spite of this being a small rural school where pretty much everybody knew everybody, I didn't recognize her, and anyway she seemed a bit too old to be a high school student. She also seemed somehow more brightly lit than her surroundings, and had a vaguely unreal aspect to her, like my eyes weren't able to get her fully in focus for some reason, almost as if I was viewing her through a heat distortion. Her expression, from what I could make out through the blurriness, seemed intense, and as I stared at her, she seemed to slowly shake her head no.
While fervently trying to decide whether this was a trick of my imagination, or if this strange woman was actually somehow aware of what I was about to do and was silently warning me not to, I suddenly realized something, and surreptitiously opened my bag to check. Sure enough, the sex book was not, as I had been assuming, someone's misplaced personal stash, but an official school library book, and on the inside of the back cover was a white circuit sticker, the kind that sets off anti-theft alarms. If I had not been brought up short by the woman's glare and had attempted to walk out, the alarm would have gone off, the librarian would have searched my bag, and I would have been caught with pornography in front of God and everybody.
I returned the book to its hiding place and then hightailed it out of there, shaky and relieved.
Guardian angel, or just a combination of guilty conscience, subconscious realization, imagination, and coincidence? I don't know, but I never saw that woman again.