Lieutenant-Commander Oliver Dunbar and the crew of E-17, thirty men and boys in a steel cylinder a hundred and eighty feet long, must penetrate the Dardanelles and the Bosphorus and get into the Black Sea. The inland sea has been an Ottoman lake for hundreds of years. It's their job to sink the ships that sustain the Empire, in support of an imminent campaign on the Turkish mainland. Lined with shore batteries and some very big guns, the straits are a dagger pointed straight at the Sublime Porte. With submarine nets, mines and enemy warships everywhere, they'll be lucky to make it out with their skins intact.