‘When my contact in Germany asked for military maps of the coastline, activity of naval vessels, diagrams with coordinates of the local shipping hazards – the sandbank and so on – I knew that there was only one man around here in a position to provide them. And I knew he couldn’t be bought by the Nazis at any price. So I started digging . . . I looked in the marriage register – and I struck gold straight away. No one attended your parents’ wedding except two family members from your mother’s side: her aunt and her cousin, Max. They were both witnesses for the marriage and so their full names are in the register. My contact in Berlin recognized the cousin’s name straight away. He is in Hitler’s Gestapo now – a very powerful man – and your stupid mother had been sending him birthday and Christmas cards right up until last year.’

The man with the little blond beard . . . So there had been another reason for hiding the wedding photograph, then. It could have been used as evidence against Mutti – evidence that she was in contact with a member of the Nazi secret police.

‘This placed your family in a very vulnerable position indeed.’ She chuckled oddly. ‘I sent an anonymous letter to your father, demanding that he deliver the required information to our pick-up point, or your mother’s contacts with Hitler’s government would be exposed – to the police and to the press. Your father, I’m delighted to say, was very compliant.’

So Pa had been blackmailed. He had had no choice. Even when Pinstripe had given him the chance to tell the truth, he had refused, preferring to die a traitor than to endanger Mutti by revealing the truth about her cousin Max.

‘And your mother even confessed! The perfect scapegoat, walking herself willingly to the slaughter – very obliging of her!’

‘But the police know it wasn’t her. That detective from London – he knows it was Pa. And soon they will know that you were the one behind it all.’

‘How will they know, Petra? Who do you think is going to tell them?’ As she spoke, the beam of light swept over the sea and I thought I saw something – a little shoal of shapes, dark against the shining water. Could those be the landing craft from the U-boat?