Somebody Else's Daughter by Elizabeth Brundage
I don't know how to accurately summarize the plot of this mesmerizing novel, other than to throw out words: private high school, adoption, blended families, secret pasts, new loves, old loves, scandal, sex, drugs, history...
I really don't know how to summarize it, but I can tell you this is a totally engaging read. It took a few pages to get my attention, but then I was completely pulled into the lives of a small town in New Hampshire as old and new lives collide and clash, sometimes with happy, and more often with very unhappy results.
This is a beautifully written, well told, twisty, turny novel that I devoured. Recommended!