‘Don’t be ridiculous,’ I retorted, roused by righteous anger. ‘The last time Mr Rapoport set foot in synagogue was on his barmitzvah, eight years ago this month. The alarm, I happen to know, was installed only the year before last. Anyway, he would never defile sacred objects. He is too . . . superstitious . . . for that. Is that the best you can come up with, Inspector, a Jewish inside job?’

‘Just a theory,’ said the inspector softly, rising to let me go.

Angry as I was, I was also unsettled. A seed of doubt had been planted in a field of misery. I raced home to search the drawer where Dovidl kept his bombsite loot, in search of silver Torah bells and pointers. Nothing there, just the trinkets he had kept from the Blitz. They seemed worthless now, without him. After dark, I cycled down to Elgin Avenue to examine our secret tree-hole. Nothing there, either. Suspicion, though, is a persistent rash. I could not purge my friend’s memory of its itch.

I extended my enquiries worldwide. I wrote to my supervisor from Cambridge who had gone to teach at the University of Western Australia, asking him to check the Perth telephone directory for a Derek and Florence Mitchell and, failing that, to search the register of births for a baby Mitchell born in the last quarter of 1948 when Florrie would have been due. What if Dovidl had noticed Florrie’s pregnancy and, having no living relatives, felt an urge to be united with his child, if it was his, in Australia? Far-fetched, I realised, but worth eliminating.

The word from Perth was grimmer than I had feared. There were no Mitchell births in the period stipulated, my friend replied, but the register of deaths contained a Florence Mitchell who had died in October 1948 of septicaemia, after suffering a miscarriage. Her husband, Derek, had remarried and was running a petrol station in Adelaide, did I require his address?

I enlisted the help of the Israeli poetaster attaché, who responded warmly and energetically. But neither the Tel Aviv immigration service nor the police had seen anyone answering Dovidl’s description, dashing my hopes that he had sought a Jewish homeland.

I wrote to my father’s ministerial contact in Warsaw and got no answer. I wrote again, with the same result. Much later I learned that the poor man had been whisked off and killed in a Stalinist purge against ‘rootless cosmopolitans’, meaning Jews.

I applied for a visa to visit Poland, but was turned down. I did my best to keep the story alive in the press, praying for a sighting, but newspapers are not renowned for their constancy. A new story had excited their attention: the sinister disappearance to Moscow of a pair of high-placed British diplomats, Guy Burgess and Donald Maclean. ‘Does your story have a political dimension?’ I was asked by a news editor.