Greg had not long been in basic training when he was summoned to the colonel’s office. ‘The Army Corps of Engineers needs a bright young officer in Washington,’ the colonel said. ‘You’ve interned in Washington, but all the same you wouldn’t have been my first choice – you can’t even keep your goddamn uniform clean, look at you – but the job requires a knowledge of physics, and the field is kind of limited.’

Greg said: ‘Thank you, sir.’

‘Try that kind of sarcasm on your new boss and you’ll regret it. You’re going to be an assistant to a Colonel Groves. I was at West Point with him. He’s the biggest son of a bitch I ever met, in the army or out. Good luck.’

Greg called Mike Penfold in the State Department press office and found out that until recently Leslie Groves had been chief of construction for the entire US Army, and had been responsible for the military’s new Washington headquarters, the vast five-sided building they were beginning to call the Pentagon. But he had been moved to a new project that no one knew much about. Some said he had offended his superiors so often that he had been effectively demoted; others that his new role was even more important but top secret. They all agreed he was egotistical, arrogant and ruthless.

‘Does everybody hate him?’ Greg asked.

‘Oh, no,’ Mike said. ‘Only those who have met him.’

Lieutenant Greg Peshkov was full of trepidation when he arrived at Groves’s office in the striking New War Department Building, a pale-tan art deco palace on 21st Street and Virginia Avenue. Right away he learned that he was part of a group called the Manhattan Engineer District. This deliberately uninformative name camouflaged a team who were trying to invent a new kind of bomb using uranium as an explosive.

Greg was intrigued. He knew there was incalculable energy locked up in uranium’s lighter isotope, U-235, and he had read several papers on the subject in scientific journals. But news of the research had dried up a couple of years ago, and now Greg knew why.

He learned that President Roosevelt felt the project was moving too slowly, and Groves had been appointed to crack the whip.

Greg arrived six days after Groves had been reassigned. His first task for Groves was to help him pin stars to the collar of his khaki shirt: he had just been promoted to brigadier-general. ‘It’s mainly to impress all these civilian scientists we have to work with,’ Groves growled. ‘I have a meeting in the Secretary of War’s office in ten minutes. You’d better come with me, it’ll serve you for a briefing.’

Groves was heavy. An inch under six feet tall, he had to weigh two hundred and fifty pounds, maybe three hundred. He wore his uniform pants high, and his belly bulged under his webbing belt. He had chestnut-coloured hair that might have curled if it had been grown long enough. He had a narrow forehead, fat cheeks, and a jowly chin. His small moustache was all but invisible. He was an unattractive man in every way, and Greg was not looking forward to working for him.