Joe O’Byrne owes two long-dead German twentysomethings a debt of gratitude. But not solely that, he says; he also owes them what he calls “a debt of exactitude”. His second World War novel The Red Orchestra in Blue – published on the 80th anniversary of VE Day – is a fictionalised account of young couple Harro Schulze-Boysen and Libertas Haas-Heye as they evolve from being the cultured darlings of Berlin society into fearless resistance fighters. Once welcomed in elite Nazi circles (aristocrat Libertas was given away by Hermann Göring at their 1936 wedding), this extraordinary pair became part of the...