"June 1940. Britain is Europe's final bastion of freedom - and Hitler's next target. But not everyone fears a Nazi invasion...

In factories, offices and suburban homes are men and women determined to hasten it. Throughout the Second World War, Britain's main defence against the enemy within was Eric Roberts, a former bank clerk from Epsom. Equipped with an extraordinary ability to make people trust him, he became Hitler's man in London - while really working for MI5.

Codenamed Jack King, he single-handedly built a network of British Nazi sympathisers, with many passing secrets to him in the mistaken belief that he was a Gestapo officer.

Agent Jack shatters the comfortable notion that Britain could never have succumbed to fascism, and celebrates - at last - the courage of individuals who protected the country they loved at great personal risk."