Corruption - The Bureau, #1

Once a proud demon of the night sky who carried nightmares to humans, Tenrael has spent decades in captivity as the star attraction of a traveling carnival. He exists in miserable servitude to men who plunk down ten dollars to fulfill their dark desires. Charles Grimes is half human, half. something else. For fifteen years he's worked for the Bureau of Trans-Species Affairs, ridding the country of dangerous monsters.
When his boss sends him to Kansas to chase a rumor about a captive demon, Charles figures it's just another assignment. Until he meets Tenrael.