The Vault (The Farm #3) by Emily McKay
Berkley Trade/November 2014
In a world where vampires rule and teenaged humans are quarantined as a food source, there is only one choice—resist or die. But fighting the vampires comes at a terrible cost to twin sisters Mel and Lily and their best friend Carter . . .
With Lily exposed to the vampire virus and lying in a coma, it’s up to Mel and Carter to search for the cure. Time is not on their side. With every passing heartbeat, Mel is becoming more and more purely vampire.
Desperate, Carter and Mel decide to split up. Carter will recruit human rebels from the Farm in San Angelo to infiltrate the guarded kingdom of the vampire Sabrina and steal the cure. Mel will go back to her mentor, her friend, her betrayer, Sebastian, who is the only one who can access an underground vault that may house the secret to the cure.
That is, if he’s still alive after she staked him to the ground. Now her worst enemy may be their best hope for curing Lily—and saving the human race.