The fateful duel of 1809 between Lord Castlereagh and George Canning is one of the great puzzles of 19th-century British politics. What made these two titans of the political scene - close colleagues and both highly effective members of the Cabinet - draw arms against each other? Canning was Foreign Secretary while Castlereagh was Secretary of State for War and the Colonies: what were they thinking on that ominous morning and what was important enough to provoke two Cabinet ministers to such extraordinary behaviour?This detailed history of the famous duel is the first to examine fully the careers of these two great men and the political conflicts that brought them to fire shots at each other on Putney Heath. Drawing on previously overlooked private papers, Giles Hunt traces what happened on that eventful day and its consequences for British politics. Castlereagh is traditionally depicted as an old-fashioned Tory reactionary, Canning as a brilliant but ambitious liberal. The Duel analyses how much truth there is in these descriptions and examines the roots of the political and personal rivalry which led these two men to face each other with pistols early in the morning of 21st September 1809 in one of the strangest and most significant duels of history.