The Second Secretary of the Embassy in Istanbul has died in decidedly strange circumstances while attempting to swim the Dardanelles Straits, the passage between Europe and Asia, heavily used by warships, liners, and cargo vessels of all kinds. A romantic attempt to repeat the legendary feat of Leander, as the Embassy claims? Or was it an attempt to spy out a possible landing place for a British military expedition, as the Turks are insisting? Whichever, Cunningham has ended up with a bullet in his head.

The suspicious circumstances of his death have to be investigated so the Foreign Office sends out an officer of the Special Branch known as Seymour.

Istanbul is a fascinating and exotic place in 1908. It is famously the point where East meets West, a matter of some significance as the old Ottoman Empire crumbles and, in the expectation of war, the Great Powers circle for the kill. Very soon Seymour comes to suspect that Cunningham may have been swimming in deeper waters than the Dardanelles.