Lesser Evils

First there were three.

''Mere weeks after escaping Neverwinter, Farideh's dreams are still haunted by Lorcan, the cambion devil whose power fuels her own. One of only four known descendants of the original Brimstone Angel, Farideh has no regrets about the pact she made with the devil. But no one in the Hells knows that she has a twin - an impulsive, eager sister just waiting to be corrupted. At least as long as Lorcan can keep her secret.''

And then you found the fourth.

Determined to protect her sister, Farideh searches for a ritual that could call Lorcan out of the Hells, but in the midst of her hunt, she's drawn into an assignment for the secret society of the Harpers, an assignment which leads her and a ragtag group of allies to an ancient Netherese library deep underground.

The fifth one is mine.

''While the group combs the site, dodging ghosts and magical traps, Farideh discovers a magical book whose pronouncements throw into question everything she thought she knew about herself and her sister. The more the Book gives up its macabre secrets, the more one thing becomes clear - a traitor lurks among them.''

The fifth Brimstone Angel.