A middle-aged Irish immigrant, Billy has a gift for illusion—making damaged objects look new. His companion, Charles, the smooth-tongued teenage son of a prostitute, is a natural salesman. Longtime horse traders and partners, they’ve recently turned their talents to trading mules. But in the summer of 1916, these seasoned grifters have just been swindled themselves. They’re saddled with the one thing they may not be able to unload: a gorgeous, murderous black mare named The Midnight Cool.

Charles should have listened to Catherine, the beautiful, rebellious daughter of Leland Hatcher, the former owner of The Midnight Cool. The horse would be worth a fortune—if she weren’t a verified man-killer who attacks on sight. Charles and Billy must now miraculously retrain this mysterious mare, but their bond begins to fray when Charles falls in love with Catherine and resolves to make a settled life for himself.

The Great War in Europe has pushed demand for mules sky-high, and when America enters the fight in 1917, the two men become town heroes, supplying Tennessee mules to the Army. But in the fervor of patriotism, xenophobic paranoia, and the strengthening grip of war, Charles is forced to question his ideals, and when a trade goes terribly wrong, he must choose between freedom and responsibility, self and country, and, ultimately, duty and love.