The Head of the Dog (Merchant #3) by Chris Miller
Sam Merchant is no fan of Christmas, but the holiday gets worse when he witnesses his latest client get murdered in front of his office. The police are worthless, and Merchant wants answers, so he sets out on his own to find the killer.
After discovering the murder weapon--a strange knife with odd carvings on its hilt--he soon finds himself at the center of a sinister plan to bring something monstrous into the world. It's up to Merchant, Charlie, and Blanche to put a stop to the madness, but these animals don't play. Will they be able to stop the killers and save the world, or will they fall prey to The Head of the Dog?