Queen of the Damned: Imp Series, Book 9 (Unabridged‪)‬

The ancient demons of Hel have awakened, and one of them is gathering forces for an invasion of Aaru - which is pretty hilarious as far as Sam is concerned. Few know that Aaru is locked down tight after she banished all the angels. Nobody can get in. Nobody. Well, maybe nobody. The one being in Hel that might be able to restore Aaru is the archangels' prodigal brother. But he's presumed dead, having not been seen in over two million years. The remote possibility of an attack on Aaru isn't Sam's only problem.

Lows are being snatched off the streets of Dis, and hauled away to the home of an ancient demon never to be seen again - and a few of the missing Lows belong to Sam's household. Suddenly Sam finds herself providing sanctuary in her earthly home for all the Lows in Hel. She'll need to go undercover to discover if there's anything to be concerned about in this planned Aaru invasion as well as find the Low-snatcher and somehow persuade him at the point of a sword to leave the minor demons alone before her home is overrun with refugees.