The first 75% was a 5 star read but stars have to be deducted for: 
 1) (view spoiler)[the obvious twist with Samantha being Cecily (hide spoiler)] 
 2) (view spoiler)[Gabriel magically regaining his sight (hide spoiler)] 
 2) (view spoiler)[the change in character experienced when Samantha leaves and goes back to being Cecily - it meant it was very difficult to actually see them as the same character at all (hide spoiler)] 
 3) (view spoiler)[Gabriel not guessing that Samantha was Cecily (hide spoiler)] 
 4) (view spoiler)[Gabriel not guessing that Cecily was Samantha - and it's not like their meetings were fleeting, they had whole conversations and sex and he still had no idea (hide spoiler)] 
 5) (view spoiler)[Unknown cheating from Gabriel - see above spoiler (hide spoiler)]