‘Sir Carmichael Clarke was an immensely wealthy man. Who inherits his money? His wife, who is dying, has a life interest in it, and it then goes to his brother Franklin.’

Poirot turned slowly round till his eyes met those of Franklin Clarke.

‘I was quite sure then. The man I had known a long time in my secret mind was the same as the man whom I had known as a person. A B C and Franklin Clarke were one and the same! The daring adventurous character, the roving life, the partiality for England that had showed itself, very faintly, in the jeer at foreigners. The attractive free and easy manner—nothing easier for him than to pick up a girl in a café. The methodical tabular mind—he made a list here one day, ticked off over the headings A B C—and finally, the boyish mind—mentioned by Lady Clarke and even shown by his taste in fiction—I have ascertained that there is a book in the library called The Railway Children by E. Nesbit. I had no further doubt in my own mind—A B C, the man who wrote the letters and committed the crimes, was Franklin Clarke.’

Clarke suddenly burst out laughing.

‘Very ingenious! And what about our friend Cust, caught red-handed? What about the blood on his coat? And the knife he hid in his lodgings? He may deny he committed the crimes—’

Poirot interrupted.

‘You are quite wrong. He admits the fact.’

‘What?’ Clarke looked really startled.

‘Oh, yes,’ said Poirot gently. ‘I had no sooner spoken to him than I was aware that Cust believed himself to be guilty.’

‘And even that didn’t satisfy M. Poirot?’ said Clarke.

‘No. Because as soon as I saw him I also knew that he could not be guilty! He has neither the nerve nor the daring—nor, I may add, the brains to plan! All along I have been aware of the dual personality of the murderer. Now I see wherein it consisted. Two people were involved—the real murderer, cunning, resourceful and daring—and the pseudo murderer, stupid, vacillating and suggestible.

‘Suggestible—it is in that word that the mystery of Mr Cust consists! It was not enough for you, Mr Clarke, to devise this plan of a series to distract attention from a single crime. You had also to have a stalking horse.

‘I think the idea first originated in your mind as the result of a chance encounter in a city coffee den with this odd personality with his bombastic Christian names. You were at that time turning over in your mind various plans for the murder of your brother.’

‘Really? And why?’

‘Because you were seriously alarmed for the future. I do not know whether you realize it, Mr Clarke, but you played into my hands when you showed me a certain letter written to you by your brother. In it he displayed very clearly his affection and absorption in Miss Thora Grey. His regard may have been a paternal one—or he may have preferred to think it so. Nevertheless, there was a very real danger that on the death of your sister-in-law he might, in his loneliness, turn to this beautiful girl for sympathy and comfort and it might end—as so often happens with elderly men—in his marrying her. Your fear was increased by your knowledge of Miss Grey. You are, I fancy, an excellent, if somewhat cynical judge of character. You judged, whether correctly or not, that Miss Grey was a type of young woman “on the make”. You had no doubt that she would jump at the chance of becoming Lady Clarke. Your brother was an extremely healthy and vigorous man. There might be children and your chance of inheriting your brother’s wealth would vanish.