There is a fifth element that is just starting to be uncovered; the powerful but dangerous element known as spirit. Lissa is one of the few Moroi who can use it. When Lissa, her family and Rose were in a car accident Lissa used spirit to bring Rose back from the dead. Unknown to Lissa this would bind her and Rose together forever and make Rose Shadowkissed, someone between life and death. Rose's bond to Lissa allows her to experience what her friend sees and feels which comes in useful as Rose takes on her role as Lissa's Dhampir and protector.
Through their bond we get the learn a lot about Rose, Lissa, their relationship as well as their relationships with other characters. This series has excellent character development, especially for Lissa and Rose as they both go on their own journeys. Other characters are introduced in each book while the regulars such as Eddie and Christian develop more. The bond between Lissa and Rose is one of the strongest bonds of sisterhood I have read about. They have and would die for each other. Their bond is one reason why this series is one of my favourites.
The world is full of mysteries that we learn more and more about as Rose explores the world. There are mysteries that even the Moroi and Dhampirs don't know about which Lissa and Rose uncover. The mystery of their bond and Lissa's abilities is the main part of the series which is very interesting to learn about.
This series is action packed, full of suspense, twist, turns and magic. It is written really well and fast passed. I love this series. The magic and mysteries alone are great.