After Kaz sent Kent to kidnap Melissa in Double Sides, she was taken to The Demon's Fortress and injected with demon blood. Melissa managed to escape and was hiding in the forest in a fragile state when The Queen of Thieves found her and tried to help her.
The demon blood injected into Melissa by Morgan Roots had turned her into a demon-like creature by that point. Unknown to her the angel blood inside her stopped her from transforming into a full demon, but the side-effects caused her to develop multiple personalities creating Vanessa, an evil form of Melissa.
Melissa's personality changed after she developed into Vanessa. She had turned cold and distant, no longer caring for her friends the way she did. She also had a new-found ideology, closely following that of Kaz and the Demon. Now that she was Vanessa she had turned rather bloodthirsty wanting to harm those who were once her friends her soul had turned dark due to the demon blood pulsing through her veins
Due to being injected with demon blood, Melissa gained new abilities as Vanessa. Vanessa has keen senses of hearing, eyesight, and movement.
- Kaz used Vanessa to his advantage since she was a loved member of the group to cause greater harm to everyone.
- Jen Devlin, having re-established contact with her daughter, Melissa, after years of not seeing each other, helped the group find a way to cure Melissa before she was gone forever and only Vanessa was left.