Submit dives more into the relationship of Jonathan and Monica.
Monica is struggle with everything that she believes that she is not. She just can't she herself as a submissive, yet she doesn't want to give up Jonathan either.
Trouble is ensured and a life altering event will effect Monica more than she wants to admit to herself.
I can really say to much without giving everything away. If you want to know what happens, you will have to read it for yourself.