The Duchess of Skid Row (1960) by Louis Trimble

When Special Investigator Jeff McKeon was called hurriedly back to the Puget City DA's office, it marked the end of a beautiful vacation and the abrupt beginning of an ugly frame. For while Jeff's back had been turned, his political enemies had been busy laying plans to give him a permanent vacation—in jail. This time they had the DA on their side, for the evidence seemed quite foolproof. Jeff, they convincingly demonstrated, was the new front-man for the Syndicate's big push into town. And when Jeff realized he had to tackle the Syndicate itself to disprove that, he knew that his fate now lay in the fickle hands of The Duchess of Skid Row —a gal who had every reason to want him dead.