A Doorway into Ultra by Susannah J Bell
Claire was taken as a small child and returned seven years later. With no memory. Even though DNA tests confirm her parentage her father knows she isn’t his true daughter and her mother has great difficulty relating to her. Knowing she doesn’t belong with them, feeling she belongs with a man she has glimpsed only fleetingly, Claire runs away to find him. The plot thickens when, on spotting this man’s double, unlike the now familiar original one, he shows no recognition of her. What is the connection between that fact and the powerful feeling of having a twin? This is a fascinating scenario with an intriguing plot, beautifully penned and well worth reading.
I was led from fear of just another alien abduction story, through a number of alternative explanations and… Well, no spoilers other than, it had a good twist.