The Regina Palast was an immense, monumental gray stone cube of a hotel, built in 1908, with Versailles-style reception rooms, a Turkish bath in the basement, and three hundred bedrooms arranged over seven floors, of which the British delegation had been allotted twenty. These ran along the front of the hotel on the third floor, with views across the trees of Maximiliansplatz to the distant twin Gothic spires of the Frauenkirche.

After the prime minister and his team had left for the start of the conference, Hugh Legat spent the next ten minutes walking up and down the dimly…