For Want of a Nail. Of course we all know Gentleman Johnny Burgoyne won the Battle of Saratoga, and as one of the pivotal battles that sunk the attempted American revolution, this led to the overall British victory. Cue this book, a literal alternate history of the events that followed.
What makes this book particularly effective is it's written in a perfectly appropriate style, that of a historian producing a comprehensive work of history, with plenty of clarity and a slightly dry tone, and to complete the illusion, the book has footnotes and references to fictional works, and a bibliography that is likewise entirely invented. The only thing letting the book down in this respect is the subheading; it should have been 'Burgoyne's Victory at Saratoga' or similar, to hook the history buffs and leave the ignorant undisturbed, but one cannot have everything.
Contained within this masterful work of duplicity, lies an entertaining alternate history of North America that has been constructed with care and attention to detail. Best textbook evar.