Benedict Arnold was different: a military hero for both sides in the same war. He began his career as an American Patriot in May 1775, when he and Ethan Allen led the brigade that captured Fort Ticonderoga on Lake Champlain. Arnold's heroics continued in September, when he led an expedition of 1,150 riflemen against Quebec, the capital of British Canada. The American commander drove his men hard through the Maine wilderness, overcoming leaky boats, spoiled provisions, treacherous rivers, and near starvation to arrive at Quebec in November, his force reduced to 650 men. These losses did not deter Arnold. Joined...