It's this one. George Washington is one of my heroes and the story of his coming out of his "retirement" from public life in order to preside over the Philadelphia convention that hammered out the U.S. Constitution is a story worth telling. I'll have to wait awhile before reading it though.
(Thanks to Glenn Reynolds for mentioning that he had just ordered the book. That's not an endorsement of Reynolds' quirky politics, by the way. I read a bit of everything when I have the chance. Reynolds has been kind in linking to some of my blog posts in the past.)