‘My grandmother grew up brushing her teeth with radioactive toothpaste’ is the arresting opening sentence of Joe Dunthorne’s family memoir. The reason for such a strange practice? Her father was an experimental chemist, and he was enthusiastic about the possibilities of radiation. His name was Siegfried Merzbacher and he was director of a secret laboratory for the development of chemical weapons at Oranienburg. Siegfried and his family were German Jews. Dunthorne believed that they left Germany in 1935 and emigrated, as many German Jews did, to Turkey, where his great-grandfather took up humanitarian work with the Turkish Red Crescent. It turns out it wasn’t quite like that either. Bit by bit, doing research (helped along by his mother, who reads and speaks German), taking himself to the relevant locations and talking to archivists and activists, he uncovered some deeply uncomfortable truths.

Dunthorne begins with Siegfried’s unpublished memoir. It runs to some two thousand pages and, so far as he can tell, nobody in the family has read it through because it is deeply boring. Nonetheless he gives it a go. He notes that it is broadly informative, although not on the period most of interest to him, and that Siegfried habitually turns from ‘difficult episodes’ to describe a soothing holiday. 

Even someone unfamiliar with German history would know that for a Jewish chemist working on behalf of the Nazis in 1933–5 the number of difficult episodes would have rapidly increased. Why did Siegfried not write about them? This is a story of cumulative denialism. How far the denial was