Althea Duchannes is the daughter of Katherine Duchannes, sister of Emmaline Duchannes and the aunt of Sarafine and Delphine. thus being Lena and Ridley Duchannes' great-aunt. She was a Dark Evo, meaning she can morph into anyone she wanted and could also control whoever she wanted, like a Siren.
When she turned sixteen and was Claimed by the Dark, her mother couldn't stand to send her away, and tried to keep her daughter with her, but eventually she was forced to after people in town got injured and a girl drowned, it became obvious that there was no turning back. Since then, they can't live with their parents until they're Claimed.
As an Evo, she was an incredibly powerful Caster. She could control someone and influence them to do whatever she wanted, like a Siren, and could morph and sound like anyone she wanted. Also being an Evo, an extremely powerful Caster, she had the ability to Kelt and borrow the powers of any Caster she touched.