He’d first visited the place when he was three or four, and he and his mother would spend the whole of August there every year, so by the time he was sixteen, he’d been there a dozen times, becoming quite fluent in the language. His memories of the city were predominantly of the interminable train journeys to and from the country across northern Europe, the stifling formality of his grandparents’ house, and Sundays spent at a series of services in the local Lutheran church. The smell of mothballs surrounded his grandfather, while his grandmother appeared to have sprayed her clothes in especially pungent lavender.

His grandfather had been a clerk at the enormous Carlsberg brewery in the centre of the city, but as he had worked his way up in the company, the family had moved in a similar direction through the more middle-class suburbs to the north of city. For most of Prince’s childhood they’d lived in Hellerup, and his grandmother – not someone given to any obvious displays of emotion – found it hard to conceal how thrilled she was to be resident in such a smart area.

But the atmosphere in the house was a difficult one. Prince was forced to drink sour milk, which his grandmother insisted was good for him, and his grandparents were forever criticising both him and his mother. Nothing she did was good enough, and behind closed doors there were muffled arguments most evenings. She would often come to check on him in his bedroom afterwards, her eyes moist with tears, and occasionally she would make a remark along the lines of ‘Maybe now you can understand why I left Denmark.’

The visits ceased in 1925 following his grandparents’ deaths from influenza within days of each other. Prince’s mother barely managed to disguise her relief. The last time he’d been to Copenhagen was in 1928, when he was twenty and already a sergeant. It was his cousin’s wedding, and he and his parents flew from Croydon Airport to Amsterdam and from there on to Copenhagen on one of Danish Airlines’ new four-engined Farmans. And now he was back.

For someone who claimed he liked to have company, Egon had been surprisingly taciturn during the two-hour drive to the city. Prince reckoned he must be nervous; it was something he’d picked up with other members of the resistance since he’d arrived in Denmark. As benign as the German occupation was, helping a British agent was still punishable by death.