“Sorry. Ethically challenged practitioners,” said Nightingale. “My first ‘governor,’ Inspector Murville, had handled a notorious case in Limehouse in 1911. It involved a famous stage magician working under the name of Manchu the Magnificent who had collected some very strange ‘people’ and was using them to carry out his nefarious plans.”

“And his nefarious plans were what, exactly?” I asked.

“Nothing less than the overthrow of the British Empire itself. Apparently, Inspector Murville, as he set off on his crusade, had it on good authority that Manchu the Magnificent operated an opium den on the Limehouse Causeway. There the yellow devil sat like a fat spider at the center of a web of plots, white slavery being merely the start of it.”

“What’s white slavery when it’s at home?” I asked.

Nightingale had to think about it a bit but apparently when he was young white slavery mostly referred to the trafficking of white women and children for the purposes of prostitution. The inscrutable Chinese were supposedly behind this dastardly trade in lily-white female flesh. I wondered if part of the outrage came from a guilty conscience. I said as much.

“There were established cases, Peter,” said Nightingale sharply. “Women and children were bought and sold in beastly circumstances and suffered real hardship. I doubt they found the historical irony much comfort.”

Inspector Murville, convinced of the seriousness of the threat, organized a raid with half the available wizards in London and a mob of constables loaned to him by the commissioner. Cue a great deal of banging down doors and shouting of “Hold still, you Oriental devil” and then a certain amount of stunned silence.

“The Great Manchu the Magnificent,” said Nightingale, “was revealed to be a Canadian by the name of Henry Speltz. Although he was married to a Chinese woman with whom he had five daughters, all of whom had acted as his beautiful assistant ‘Li Ping’ at one time or other.”

Nothing was found at the house except for a strange young European girl who lived in the household and worked as a maid. Under caution Speltz told Inspector Murville that the girl, whom nobody in the household had thought to name, had been found cowering in one of his disappearing cabinets at the end of a matinee performance at the Hackney Empire.

I mopped up the last of the onion gravy with the last bit of bread in the basket. Nightingale had left half his pudding untouched. “Are you going to finish that?” I asked.

“Help yourself,” said Nightingale, and I did while he finished the story.

Some things never change and a senior police officer doesn’t organize a costly raid and admit to failure, or violating the Magna Carta, until he’s done his best to convict someone of something. Had Speltz actually been Chinese, things might have gone very hard for him. But in the end he was formally charged with disturbing the peace and let go with a police caution.