It turns out that right before Rob (Adele's friend) died that mysterious death he had switched bodies with Adele. He had met Adele's husband, David at the psychiatric facility where he and Adele were getting treatment. Rob became obsessed with David and right after he switched bodies with Adele, he killed her (himself?) Then when he killed himself (as Adele) he switched bodies with Louise right before Adele died. So really it was Louise who died and not the soul inhabiting Adele.
The book ends with Louise and David getting married and "Louise" plotting ways to kill her son so he doesn't give it away.
CLICK HERE TO READ FULL REVIEW