Sir Edward Grey is remembered largely as Britain's Foreign Secretary when ‘the lights went out all over Europe’ in the summer of 1914. His record remains contested. From David Lloyd George's crafty deception in his wartime memoirs to more recent revisionist historians, writers have sought to blame Grey for the outbreak of the First World War. Drawing on substantial research in private and official, British, and foreign archives, this paper will reconstruct Grey's career as Foreign Secretary with an emphasis on his objectives and the means which he employed to obtain them. Crucially, it places Grey's stewardship of British foreign policy within the broader international context, defined by the steep decline and subsequent renaissance of Russian power in the years between 1905 and 1912/13, with the aim of establishing the limitations of British power. More especially the shift in the international balance around 1913/14 shaped towards Russia, and away from Germany, shaped Grey's calculations during Europe's last summer. The July Crisis showed both the strengths and the limitations of Grey's diplomacy, this persistent and subtle pressing for mediation, but also his misreading of Austro-Hungarian policy.