Harlan Coben wrote a masterpiece in this novel.But I would say there is a fatal flaw in the plot premise.When the scion of the rich family had gotten to "know" it was not his crush Rachel who mothered the child thus had his plan frustrated, then why did he go ahead and steal the child anyway?
And there is this technical thing.If David was the real biological father,then his wife must have been impregnated by his sperm.So how could his wife have gone through with fertility clinic procedure?Clinic must have detected that her ovum had already been enseminated.