Feel free to climb down from the brain racks -- the total bewilderment from all quarters which has greeted my enquiry has convinced me that I was probably imagining the whole thing, and that the idea I've outlined is actually original to me. Either that, or that I've nicked it from an author so obscure that nobody's going to notice the borrowing in the novella either.
Of course, I've now given away the ending of the novella to around 95% of the people who actually care. And knowing my luck the first review to appear will say, "The major flaw in the novella is Purser-Hallard's blatant and unacknowledged borrowing from Myron Parboil's The Dominatrices of Time", and I'll immediately bang my forehead and shout "Of course it was bloody Myron Parboil! How could it possibly have been anyone else?".
Which will be unfortunate, but will at least provide some closure for my current sense of unresolved frustration.