With a genius for guerrilla warfare, Mosby diverted enemy troops from the front and used fear as a psychological weapon. For more than twenty-seven months he led daring overnight raids behind Union pickets and created false alarms up and down the Potomac. Although Mosby never commanded more than 400 men, his forces were regularly overestimated, once by a factor of forty. Union officials dispatched more than seventy search and destroy missions against him personally, but he retained the tactical advantage until Lee's surrender at Appomattox.

Mosby's dynamic, double-sided personality, forged in childhood, was the foundation for his success as a guerrilla chief, but it was also his greatest weakness. Attempting to repeat patterns of heroic conflict after the war, he threw away his status as a leading southern hero and sacrificed a lucrative law practice to support the Republican party and U.S. Grant's campaign for the presidency.

Forced into exile from his native Virginia, Mosby frequently charged into controversy. He crusaded for truth and justice as consul to Hong Kong, acted as a federal land agent in the U.S. Midwest, authored an account of Jeb Stuart's role in the Confederate loss at Gettysburg, and served as a Justice Department attorney.