Resistance: The Underground War in Europe, 1939–1945 by Halik Kochanski Penguin, 960 pages, £35
In 1943, Polish resistance fighter Jan Nowak was on his way back from a secret meeting in Warsaw when he was stopped in the street by a Gestapo agent. The policeman demanded to know where Nowak had just been, so he pointed to the first thing he saw: the brass plate for a dentist’s surgery on the door next to him. Suspicious, the German agent rang the doorbell to confirm Nowak’s story. When the dentist came to the door she did not hesitate for a second: even though she had never seen him before, she immediately confirmed that Nowak was her patient, and the Gestapo agent reluctantly let him go.