Two men have been enlisted to kill the head of the Gestapo. This is Operation Anthropoid, Prague, 1942: two Czechoslovakian parachutists sent on a daring mission by London to assassinate Reinhard Heydrich, chief of the Nazi secret services. His boss is Heinrich Himmler but everyone in the SS says 'Himmler's brain is called Heydrich', which in German spells out Hhhh. All the characters in Hhhi are real. All the events depicted are true. But alongside the nerve-shredding preparations for the attack runs another story: when you are a novelist writing about real people, how do you resist the temptation to make things up?