Synopsis of the novel Vampire Diaries - The Return: Shadow Souls
A penitent Damon, along with Elena and Matt, follows Stefan into the Dark Dimension in an attempt to set him free from the prison he has been tricked into instead of the salvation he was seeking. When Matt sees Elena and Damon getting too close he turns back and sends Bonnie and Meredith to inform Elena what's happening back home.
Bonnie and Meredith join Elena as all three are forced to enter as slaves; the chained and leashed property of a vampire – Damon. Elena Gilbert is once again at the center of magic and danger beyond her imagination. And once more, Stefan isn't there to help. Elena is forced to entrust her life to Damon, the handsome but deadly vampire who wants Elena, both her body and soul.
They must journey to the slums of the Dark Dimension, a world where vampires and demons roam free, but humans must live as slaves of their supernatural masters. During this time, Elena becomes closer to Damon. She and Damon exchange blood many times throughout the book (in some very steamy ways) and in turn finds she has true feelings for him, adding a choice to her already mixed up life: Which brother does she really want? Stefan is imprisoned here, and only Elena can free him by finding the two hidden halves of the kitsune key to his cell. Damon, Elena, Bonnie, and Meredith must all fit into the world of the Dark Dimension and venture into its deadly high society. Only by these means may they be able to find Stefan's keys to release him and then Elena will be able to reunite with her soulmate.
While this is going on, back home Matt is hiding from the law and trying to fight the evil kitsune who are destroying the very core of their community. Matt enlists the help of the local doctor and her nephew, the boarding house owner, and Isobel's grandmother, who was once a priestess, to keep their home together until Elena, Stefan, and Damon return. Elena and Damon go down to Stefan's prison and free him. Elena feeds him her blood as they try to make it home alive.
As they leave, a good kitsune gives Elena a bouquet "For Stefan". Elena later finds out the gift she got from the Kitsune is a flower that can turn a vampire into a human. When getting back to the boarding house Damon's curiosity gets the better of him and the flower turns him human with one smell. The flower was from a kitsune Stefan met in the Dark Dimension, and was supposed to be for Stefan, who is now stuck as a vampire, and is trying to make a better relationship for him and Elena. Damon, on the other hand, wants absolutely nothing to do with humanity, hates being a mortal and is now stuck as a human. Stefan and Damon only wish that they could switch places with each other (with Stefan as a human, and Damon as a vampire).