Krystyna Skarbek / Christine Granville: One of Britain's Most Fearless WWII Spies

Poland's Second World War produced more than its fair share of stories that sound made up. There's a bear who hauled artillery shells at Monte Cassino, and then there's Krystyna Skarbek, a countess from Warsaw who skied across a mountain range with intelligence hidden in her glove linings, talked a Gestapo officer into freeing three condemned prisoners, and remains, decades on, the longest-serving female agent Britain's wartime secret service ever fielded. She went by several names during her...