Hollow (The Immortal Archives #4)

They won't even see it coming... The pure line has flourished silently for thousands of years, their secrets unbeknownst to even their closest fellow supernaturals. But the force that wiped out their numbers in the beginning has returned to finish the job, striking against the pures with invisible monstrosities only Emily and Ruby can see. Badly outnumbered and short on time, this battle will bring about a dark and deadly reality no one is ready for.