‘But certainly they are! They fall into three categories: First, and most common, the voluntary disappearance. Second, the much abused “loss of memory” case—rare, but occasionally genuine. Third, murder, and a more or less successful disposal of the body. Do you refer to all three as impossible of execution?’

‘Very nearly so, I should think. You might lose your own memory, but someone would be sure to recognize you—especially in the case of a well-known man like Davenheim. Then “bodies” can’t be made to vanish into thin air. Sooner or later they turn up, concealed in lonely places, or in trunks. Murder will out. In the same way, the absconding clerk, or the domestic defaulter, is bound to be run down in these days of wireless telegraphy. He can be headed off from foreign countries; ports and railway stations are watched; and as for concealment in this country, his features and appearance will be known to everyone who reads a daily newspaper. He’s up against civilization.’

‘Mon ami,’ said Poirot, ‘you make one error. You do not allow for the fact that a man who had decided to make away with another man—or with himself in a figurative sense—might be that rare machine, a man of method. He might bring intelligence, talent, a careful calculation of detail to the task; and then I do not see why he should not be successful in baffling the police force.’

‘But not you, I suppose?’ said Japp good-humouredly, winking at me. ‘He couldn’t baffle you, eh, Monsieur Poirot?’

Poirot endeavoured, with a marked lack of success, to look modest. ‘Me also! Why not? It is true that I approach such problems with an exact science, a mathematical precision, which seems, alas, only too rare in the new generation of detectives!’

Japp grinned more widely.

‘I don’t know,’ he said. ‘Miller, the man who’s on this case, is a smart chap. You may be very sure he won’t overlook a footprint, or a cigar-ash, or a crumb even. He’s got eyes that see everything.’

‘So, mon ami,’ said Poirot, ‘has the London sparrow. But all the same, I should not ask the little brown bird to solve the problem of Mr Davenheim.’

‘Come now, monsieur, you’re not going to run down the value of details as clues?’

‘By no means. These things are all good in their way. The danger is they may assume undue importance. Most details are insignificant; one or two are vital. It is the brain, the little grey cells’—he tapped his forehead—‘on which one must rely. The senses mislead. One must seek the truth within—not without.’

‘You don’t mean to say, Monsieur Poirot, that you would undertake to solve a case without moving from your chair, do you?’

‘That is exactly what I do mean—granted the facts were placed before me. I regard myself as a consulting specialist.’