If Lower Manhattan’s Financial District was the center of American capitalism in the 1920s, then the southeast corner of Wall and Broad Streets was its most important junction. It was dominated by the headquarters of J.P. Morgan and Co., a financial leviathan that had come out of World War I as the most influential banking institution on the globe. Across the street stood the U.S. Sub-Treasury and the Assay Office. The bustling New York Stock Exchange was located just down the road. Rain was in the forecast for September 16, 1920, but as the bells of nearby Trinity Church rang...