Vampires Vs. Aliens, Book Six — Keith B. Darrell

They came from a dying world to steal the Earth's water, a scarce resource they need to survive but didn't anticipate resistance from the vampires. The aliens' plan would doom the human race... And with no humans or other life left on Earth, the planet's furtive vampire population would be deprived of its sole food source. Now the vampires must wage a secret war against the invaders while hiding their own existence from the humans. In Book 6, Til  Death Do Us Part, as the American government increases its brutal oppression of the Hyperion alien refugees, Courtney Cartwright makes a life-altering decision. Gaunt's failure leads to an Elder's demise. The NSA Domestic Threat Division closes in on the vampires.