Song in the Dark by P.N. Elrod

Jack has been suffering some serious ill effects from his torture by Hog Bristow, blinding headaches when he attempts to hypnotize someone, panic attacks, and other PTSD-type symptoms. He's also lost control of his feeding a couple of times (fortunately only on cattle) and has become aware of his nearly overwhelming desire to enjoy the pleasures of taking human blood instead of animals'. Charles, his best friend, and Bobbi, his girlfriend, are walking on eggshells around him, trying to help him when he won't even admit that he's got problems.

Into this situation, throw the additional complication of Gordy getting shot, and having to hide out while he recovers, putting Jack in charge of his criminal enterprise temporarily. New York has sent Whitey Kroun to Chicago to investigate the death of Hog Bristow at Jack's hands, and everyone is certain that Kroun will simply decide that Jack must "pay" for his transgression. But Jack forces himself nearly to the brink of disaster by using his hypnotic powers to convince Kroun to leave him in charge until Gordy gets well, that Hog got only what he had coming, and that he and Whitey are good friends.

The unexpected side effect of this is that Jack gains a sidekick, or so it seems, when Whitey hangs around and spends his time hanging out with Jack at his nightclub, Lady Crymsyn. Some of Gordy's henchmen aren't too thrilled with Jack's takeover, and when he steps in to stop the beating of a singer with big gambling debts, Alan Caine, he earns the enmity of the thug involved, Hoyle. Hoyle and his buddies retaliate against Jack, kidnapping him and taking him to the woods for a beating, but Jack turns the tables, and delivers his own style of beatdown, due to his vampire strength. Unfortunately, his squeamishness when it comes to killing causes him to leave the boys alive, and they continue to plague him throughout the rest of the book.

When Caine's strangled body turns up in his dressing room soon after, Jack and Whitey team up to keep the cops out of things, and to try to find out who really killed the man, who was not as popular with all the folks he owed money to as he was with the ladies, except for his ex-wife, who is on the short list of suspects, owing her many months of back-alimony.

Jack's fight against his demons, inner and outer, makes an interesting tale with a very surprising twist at the end.