Vanessa Santoro first appears at Kendra and Seth Sorenson's home. She had been sent to pick them up and take them to Fablehaven, away from Errol, who claims to be an ally, but ends up being a member of the Society of the Evening Star. Vanessa was a member of the Knights of the Dawn. She is presented as a keeper of magical creatures. She later turns out to be a Narcoblix, which is a species of Blixes who can control people whom they have previously bitten when they sleep or become unconscious. She gains trust from everyone and says that she's Kendra's "pen-pal" by giving her an umite candle so they can write each other secret messages. She is a traitor and a member of the Society of the Evening Star. Vanessa has black hair. Throughout the series, Newel and Doren are in love with the Narcoblix. She eventually turns against the Sphinx and fights alongside the Sorensons. Later, Bracken reveals that she has a crush on Warren, and they are seen sitting together near the end of the book.
Along with Errol, she is assigned by the Sphinx to retrieve an artifact from a preserve. Vanessa temporarily joins forces with Kendra and Warren in the Inverted Tower in order to defeat the Guardian Cat and secure the artifact another. During the fight, Errol gets killed and she gets coated with it acid, though she is saved by Kendra. After she admits she should be punished, she is imprisoned in the Quiet Box in the Dungeon of Fablehaven so that she cannot control anyone whom she has bitten. Before she is put into the Quiet Box she leaves a message for Kendra, telling her more about the Sphinx.
In the third book she is released for a short time in the hopes of gaining information from her. She tells them nothing, but she is willing to spill for her freedom.
In the fourth book, she is freed by a Stingbulb copy of Maddox Fisk, but chooses to help the Fablehaven caretakers capture the imposter and press him for information at the same time giving up several opportunities to rejoin the Society, return critical information to the Sphinx, although she later hates the Spinx. She is given a cell phone and is allowed to live in a cell with some efforts to make her comfortable while she uses her powers to take control of Society members she's bitten to gain information. However, this freedom comes with a warning. If she takes control of Stan, Ruth, Tanu, Coulter, Seth, Warren, Dale, or Kendra (whom she could never control in the first place) they would take it as a clear sign of where her loyalties lie and kill her. She does however break this rule and takes possession of Tanu, saving the expedition at Wyrmroost from Glommus, but given the circumstances, her intentions and the results of doing so, it's overlooked, though they still remain wary of her. Vanessa also reveals some of the inner workings of the Society, including how the Sphinx was always its leader, and claims to hold a secret so great it would likely buy her her freedom and she cannot reveal it just yet.
Vanessa helps Seth fulfill his plan he received from Patton Burgess, which included capturing Cormac the Leprechaun, negotiating with the Singing Sisters, and bargaining with the Totem Wall. She also assists in the Battle of Zzyzx. Warren Burgess is revealed to be an assumed love interest. She's around when Zzyzx opens. It is also hinted by Bracken that she used to be in love with the Sphinx in Keys to the Demon Prison.