Dark Voyage

“In the first nineteen months of European war, from September 1939 to March of 1941, the island nation of Britain and her allies lost, to U-boat, air, and sea attack, to mines and maritime disaster, one thousand five hundred and ninety-six merchant vessels. It was the job of the Intelligence Division of the Royal Navy to stop it, and so, on the last day of April 1941 . . .”

May 1941. At four in the morning, a rust-streaked tramp freighter steams up the Tagus River to dock at the port of Lisb...