At the height of Britain's 20th century power, Sir Archibald Clark Kerr reached the pinnacle of his remarkable and controversial career. He served in vital diplomatic posts and was a major figure in determining and executing British foreign policy. His vital work with Churchill, Roosevelt and Stalin is regarded as being crucial to the wartime alliance and, after the war, he was rewarded with the post of Ambassador to the US. Kerr helped develop both the Marshall Plan and the foundation of NATO and was influential in the USA and Britain's Cold War alliance. Based on specialist access to the vast Inverchapel archive, Donald Gillies argues against questions of his loyalty and addresses assumptions of his left-wing and anti-imperialist views.