: Ok, here is my theory/hope on how the 'reveal' plays out
With the paternity of her own baby in question Sam stars thinking about her own paternity, maybe she starts having dreams/flashbacks to when she was a little girl and she was playing with 2 boys (cuz John has a younger brother michael) she starts to question Alexis about her father but doesn't get anywhere, Alexis tells her after she gave Sam up for adoption she had no further contact until years later when Sam uncovered that they were Mother/daughter
Elsewhere McBain is also investigating the possibility that the sister he thought was killed in the bomb blast is actually still alive. (I say it was a bomb because McBain made reference to that to sonny about blowing people up was more HIS style, possibly another clue maybe?)
Anyway Sam and McBain's separate investigations lead them to the same conclusion simutaneously that they are siblings.
the real story...
Sam survived the bomb blast, Cody McCall found Sam alone and took her home to his wife. They were looking to adopt a baby so their mentally challenged Son could have a younger sibling but no one would adopt to them. They decided to keep Sam as their own. Sam was only 2 or 3 at the time so she wouldn't have any memory accept the subconscious ones she dreams about. And McBain wouldn't know what his sister looked like today as a grown woman.
Thomas McBain was Sam's biological father and when he found out his 'daughter' was being put up for adoption he convinced his wife they should adopt her, his wife had no idea that it was her husband biological daughter.
how'd I do?
I read somewhere, cant remember sorry. But it said something like. "What is Alexis wasnt Sam's mother?"