‘You may be, sir, but I’m damned if I am!’ said the Sergeant. ‘I mean, what can a book about some Empress or other have to do with Nathaniel Herriard’s death? It doesn’t make sense!’

‘Look here!’ Hemingway said. ‘Who was this Empress?’

‘That’s what I asked you, sir, and you ticked me off properly for wasting your time.’

‘Elizabeth. That was the name,’ Hemingway said, quite unheeding. ‘She had a son who went and committed suicide at some hunting-lodge, with a girl he wanted to marry, and couldn’t. I know that, because Mrs Herriard told me that bit.’

‘Do you mean that that might have given the murderer some idea how to kill Nathaniel?’ asked the Sergeant.

‘That, or something else in the book. Something the old lady hadn’t got to, is my guess. Wait a bit! Didn’t some foreign royalty get murdered in Switzerland, or some place, once?’

‘When would that be?’ said the Sergeant. ‘They’re always getting themselves bumped off, these foreign royalties,’ he added disparagingly.

‘It was some time in the last century, I think. What I want is an encyclopedia.’

‘Well, there’s sure to be one in the library here, isn’t there?’ suggested the Sergeant.

‘That’s what I’m hoping,’ Hemingway said. ‘And I’ve only got to find the volume I want missing to be dead sure I’m on to something!’

There was no one in the library when they entered it a few minutes later, and the Inspector was gratified to discover a handsomely bound encyclopedia on one of the bookshelves which lined the walls of the room. The required volume was not missing, and after flicking over a great many pages devoted to the lives of all the Elizabeths in whom he had no interest, and whose claims to fame he was strongly inclined to resent, the Inspector at length came upon Elizabeth, Empress of Austria and Queen of Hungary, born at Munich, December 24th, 1837; assassinated September 10th, 1898, at Geneva.

‘Assassinated!’ ejaculated the Sergeant, reading the entry over his superior’s shoulder.

‘Don’t breathe down my neck!’ said Hemingway, and carried the volume over to the window.

The Sergeant watched him flick over some more pages, run a finger down a column, and then begin to read intently. The expression on his face changed slowly from one of expectant curiosity to one of almost spellbound surprise. The Sergeant hardly knew how to contain his soul in patience, but he knew better than to intrude upon his chief’s absorption, and he waited anxiously for the reading to come to an end.

At last Hemingway looked up from the volume. He drew a long breath. ‘Do you know how this woman was killed?’ he said.

‘No, I don’t,’ said the Sergeant shortly.

‘She was stabbed,’ said Hemingway. ‘An Italian anarchist rushed up to her as she was walking along the quay at Geneva to board one of the lake steamers, and stabbed her in the chest, and made off.’

‘They do that kind of thing abroad,’ said the Sergeant. ‘Look at that King of Yugo-Slavia, for instance, at Marseilles! Bad police-work.’