Once upon a time there were twin sisters.
Very non-identical twin sisters.
One was a very outgoing, lively, adventurous person - living life to the full, and the other was not. she was trying to be good - for everyone. And the Roman Catholic demands for clean living that she had been taught and rules that she should follow to enable her to be the good person.
But this left her a dull person. Who dressed very dully and safely and prudishly. And her husband found her dull too - in and out of bed.
And then along comes a rake.
Who falls for our prude - the pure and innocent in mind and emotion if not quite body. And he awakens her from her sleep.
And through twists and turns a new life awaits Amy.
So perhaps a rather standard story line but with a twist and quite well told. Still not quite a read that grips the reader.