"That is true again," said Father Brown, nodding.
"And now, take it from the start. It lies between few people, but at least three. You want one person for suicide; two people for murder; but at least three people for blackmail" "Why?" asked the priest softly.
"Well, obviously," cried his friend, "there must be one to be exposed; one to threaten exposure; and one at least whom exposure would horrify."
After a long ruminant pause, the priest said: "You miss a logical step.
Three persons are needed as ideas. Only two are needed as agents."
"What can you mean?" asked the other.
"Why shouldn't a blackmailer," asked Brown, in a low voice, "threaten his victim with himself? Suppose a wife became a rigid teetotaller in order to frighten her husband into concealing his pub-frequenting, and then wrote him blackmailing letters in another hand, threatening to tell his wife! Why shouldn't it work?
Suppose a father forbade a son to gamble and then, following him in a good disguise, threatened the boy with his own sham paternal strictness! Suppose--but, here we are, my friend."
"My God!" cried Flambeau; "you don't mean--"
An active figure ran down the steps of the house and showed under the golden lamplight the unmistakable head that resembled the Roman coin. "Miss Carstairs," said Hawker without ceremony, "wouldn't go in till you came."
"Well," observed Brown confidently, "don't you think it's the best thing she can do to stop outside--with you to look after her?
You see, I rather guess you have guessed it all yourself."
"Yes," said the young man, in an undertone, "I guessed on the sands and now I know; that was why I let him fall soft."
Taking a latchkey from the girl and the coin from Hawker, Flambeau let himself and his friend into the empty house and passed into the outer parlour. It was empty of all occupants but one.
The man whom Father Brown had seen pass the tavern was standing against the wall as if at bay; unchanged, save that he had taken off his black coat and was wearing a brown dressing-gown.
"We have come," said Father Brown politely, "to give back this coin to its owner." And he handed it to the man with the nose.
Flambeau's eyes rolled. "Is this man a coin-collector?" he asked.
"This man is Mr Arthur Carstairs," said the priest positively, "and he is a coin-collector of a somewhat singular kind."
The man changed colour so horribly that the crooked nose stood out on his face like a separate and comic thing. He spoke, nevertheless, with a sort of despairing dignity. "You shall see, then," he said, "that I have not lost all the family qualities."
And he turned suddenly and strode into an inner room, slamming the door.
"Stop him!" shouted Father Brown, bounding and half falling over a chair; and, after a wrench or two, Flambeau had the door open.
But it was too late. In dead silence Flambeau strode across and telephoned for doctor and police.
An empty medicine bottle lay on the floor. Across the table the body of the man in the brown dressing-gown lay amid his burst and gaping brown-paper parcels; out of which poured and rolled, not Roman, but very modern English coins.
The priest held up the bronze head of Caesar. "This," he said, "was all that was left of the Carstairs Collection."
After a silence he went on, with more than common gentleness:
"It was a cruel will his wicked father made, and you see he did resent it a little. He hated the Roman money he had, and grew fonder of the real money denied him. He not only sold the Collection bit by bit, but sank bit by bit to the basest ways of making money-- even to blackmailing his own family in a disguise. He blackmailed his brother from Australia for his little forgotten crime (that is why he took the cab to Wagga Wagga in Putney), he blackmailed his sister for the theft he alone could have noticed. And that, by the way, is why she had that supernatural guess when he was away on the sand-dunes.
Mere figure and gait, however distant, are more likely to remind us of somebody than a well-made-up face quite close."
There was another silence. "Well," growled the detective, "and so this great numismatist and coin-collector was nothing but a vulgar miser."
"Is there so great a difference?" asked Father Brown, in the same strange, indulgent tone. "What is there wrong about a miser that is not often as wrong about a collector? What is wrong, except... thou shalt not make to thyself any graven image; thou shalt not bow down to them nor serve them, for I...but we must go and see how the poor young people are getting on."
"I think," said Flambeau, "that in spite of everything, they are probably getting on very well."
