The Rose Ransom (Girls Wearing Black

Relieved that the Date Auction was a success for Nicky, Jill Wentworth already has a plan for the next event in the Coronation contest: The Rose Ransom.
A strange ritual with a sordid history, The Rose Ransom sends the entire class on a hunt for a girl who has been kidnapped. Jill is certain she knows which girl will be taken and how she can locate her once she's gone.
But minutes after she sets her plan in motion, Jill gets an alert that something strange has happened at the Bloom mansion. Hacking into the mansion's security cameras, she finds a horrible scene of carnage. Three agents and one vampire were murdered during the Date Auction.
With Nicky on the other side of the world and the entire mission in jeopardy, Jill uncovers a conspiracy that could tear the Samarin clan apart, and learns that for this year's class, The Rose Ransom is much more than a game.