Dovidl was dazzled. This Lithuanian yeshiva student, untutored in science, mathematics and philosophy, had just ripped apart a riddle that regularly confounded divinity scholars at Trinity. His open-door defence of creationism was rooted in rock-solid faith, but it was supple enough to confront contemporary ideas. Where had his partner acquired such analytical skills? ‘In Vilna,’ grinned Yoel, ‘you learn logic before you can walk. The Vilna Gaon, who detested the ecstatic path of the Baal shem tov, taught that faith must be founded on iron reason. He abhorred music, mysticism and other sensual stimulants. The road to truth was paved with knowledge.’

That nearly clinched it for Dovidl. The intellectual satisfactions of Talmud – wrestling with a many-headed dispute until clarity broke through – engaged his mind with a totality that music had failed to ignite. The sensation of cracking a problem was almost hallucinogenic, raising him from mortal stupidity into a seemingly higher realm of understanding. The experience was addictive. The more he studied Talmud, the more his mind craved its fix. On fasts and days of mourning, when learning was prohibited, he felt physically deprived.

He was soon marked out as a fast-track candidate for semicha , the laying on of hands that would make him a rabbi and teacher, joining him to a continuity of textual interpretation that stretched back to Moses. His first vort, or oral dissertation before the entire yeshiva , was received with hums of approval and dart-like shafts of brilliant refutation. Oddly, to Dovidl’s Cambridge-trained mind, no one ever tested his faith. Belief in God was taken for granted. What mattered was the observance of His commandments. What did Dovidl believe? Not much, at this stage. In my view, he was a victim of post-traumatic stress disorder, acutely vulnerable to the persuasive consolations of a closed community.

Spielman came to visit him after six months, bringing news of the Medzhiner and their devastating tragedy. The Young Rebbe, newly married, had died of a brain haemorrhage at the age of twenty-four, a delayed victim of genocide. His Hassidim were paralysed by grief and fear. The Rebbe had left no child, no dynastic heir. The sect was too small to survive unled. It would have to merge with one of the greater Hassidic courts, losing its autonomy and identity, in order to preserve its melodies, its song of martyred names. There was no home, Spielman regretted, for Dovidl to return to.