Sean Lester, a Belfast protestant and Irish nationalist, became one of Ireland's first truly international diplomats when, in 1934, he took up the post of High Commissioner of the League of Nations in the Free City of Danzig, a Baltic port which both Germany and Poland coveted. Finding himself in a cauldron of intrigue, Lester made strenuous and courageous efforts to frustrate the Danzig Nazi Party's attempts to gain complete control of the city and return it to the German Reich. By mid-1936, having become virtually the only obstacle left in the way of Nazi conquest of Danzig, the Irishman soon became the focus of a very aggressive, and eventually successful campaign by Hitler and the Nazi movement to have him forced out of the Free City. As it was the only country to have official rights in Danzig, Poland's position regarding these events is crucial and perhaps was more important than that of the League of Nations itself. Extensively based on material regarding Lester from the Polish state archives never before seen outside Poland, this book examines the circumstances surrounding the Irishman's tenure in the Free City where he became one of the first western European diplomats to see the Nazi mask slip. Other primary sources used in the book are the National Archives, London, the League of Nations Archives in Geneva, Sean Lester's diary and papers and to a lesser extent German foreign ministry archives. The failure of European governments to heed Lester's warnings and to subsequently allow his 'removal' from Danzig turned out to be a missed opportunity to stop Hitler in his tracks three years before the outbreak of the Second World War. Of all the parties involved in this tale of intrigue, misjudgments and bad faith, Irishman Sean Lester is the only one to emerge with his honour intact.