WItch's Gamble (The Witches of Vegas 3) by Mark Rosendorf
"It's been nearly two hundred years since Isis, Zack, and The Witches of Vegas saved New Salem from the Wiccan vampire, Valeria. Now, Isis is a vampire and the most powerful witch in the world. Zack is also a vampire, and the president of New Salem. They thought the threat was long behind them. But Valeria escaped into the past where she set history on a horrific path.
Now, everything has changed around Isis. New Salem is destroyed, Valeria is queen of Earth, and no one has heard of Zack. To save reality, Isis must travel through time, reliving events from a history she barely recognizes, and find a way to set reality back on course. Not that she has any idea how to do that, or how to avoid the all-powerful Valeria in the process.
Isis will face challenges she can't possibly overcome, yet she must, or every single life from the past, present, and future is doomed."
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