Black Dawn (The Morganville Vampires, #12) by Rachel Caine

"With its eclectic mix of vampire and human citizens, Morganville, Texas, has always been a risky place to call home. But with the invasion of the vampire's deadliest enemy, Morganville isn't just in danger--it's dying...
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Ever since the draug--mysterious creatures that prey on vampires--took over Morganville, the lives of student Claire Danvers and her friends have been thrown into turmoil. Most of the town's residents have evacuated, but Claire, Shane, Eve and Michael have chosen to stay and fight.Using the city's water system to spread, the draug have rapidly multiplied. Things in Morganville look grim, especially since vampire Amelie--the town founder--has been infected by the master draug's bite. Now, if Claire and her friends don't figure out how to cure Amelie and defeat the draug, it looks like Morganville will become little more than a ghost town...