In December 1774, Benjamin Franklin met Caroline Howe, the sister of British Admiral Richard and General William Howe, in a London drawing room for "half a dozen Games of Chess." As Julie Flavell reveals, the games concealed a matter of the utmost diplomatic urgency, a last-ditch attempt to forestall the outbreak of war. Aware that the Howes, both the men and the women, have seemed impenetrable to historians, Flavell investigated the letters...