MB, I haven't glanced at any of the Ross books in at least twenty-five years but as plot twists go, the addition to the Collins family was pretty unforgettable. And not in a good sense.
The "professor" is the primary antagonist in the book. Elizabeth and Roger seem to go along with the charade but Mark doesn't seem to be their favorite person. Plus, there's his daughter who fortunately doesn't look a thing like dad but does bear a striking resemblance to Victoria Winters. This prompts Vicki to look further into her background. Is she Mark Veno's long lost daughter? And Veno's daughter is also interested in another Ross creation, the piano playing enigma Ernest Collins. With the sort of logic that only seems to apply in Marilyn Ross novels, the professor tries to use his mental powers to make Vicki jump off Widows Hill. Apparently he wasn't the powerful hypnotist that he thought that he was. Vicki doesn't jump. No one ends up with Ernest. Mark and his daughter depart, never to be heard from again. Vicki gets no answers. And the status quo remains in place.