“And that popular story is untrue?” suggested Flambeau.

“No,” said his friend quietly, “that story is quite true, so far as it goes.”

“Well, I think it goes far enough!” said Flambeau; “but if the popular story is true, what is the mystery?”

They had passed many hundreds of grey and ghostly trees before the little priest answered.  Then he bit his finger reflectively and said:  “Why, the mystery is a mystery of psychology.  Or, rather, it is a mystery of two psychologies.  In that Brazilian business two of the most famous men of modern history acted flat against their characters.  Mind you, Olivier and St. Clare were both heroes—­the old thing, and no mistake; it was like the fight between Hector and Achilles.  Now, what would you say to an affair in which Achilles was timid and Hector was treacherous?”

“Go on,” said the large man impatiently as the other bit his finger again.

“Sir Arthur St. Clare was a soldier of the old religious type —­the type that saved us during the Mutiny,” continued Brown.  “He was always more for duty than for dash; and with all his personal courage was decidedly a prudent commander, particularly indignant at any needless waste of soldiers.  Yet in this last battle he attempted something that a baby could see was absurd.  One need not be a strategist to see it was as wild as wind; just as one need not be a strategist to keep out of the way of a motor-bus.  Well, that is the first mystery; what had become of the English general’s head?  The second riddle is, what had become of the Brazilian general’s heart?  President Olivier might be called a visionary or a nuisance; but even his enemies admitted that he was magnanimous to the point of knight errantry.  Almost every other prisoner he had ever captured had been set free or even loaded with benefits.  Men who had really wronged him came away touched by his simplicity and sweetness.  Why the deuce should he diabolically revenge himself only once in his life; and that for the one particular blow that could not have hurt him?  Well, there you have it.  One of the wisest men in the world acted like an idiot for no reason.  One of the best men in the world acted like a fiend for no reason.  That’s the long and the short of it; and I leave it to you, my boy.”

“No, you don’t,” said the other with a snort.  “I leave it to you; and you jolly well tell me all about it.”

“Well,” resumed Father Brown, “it’s not fair to say that the public impression is just what I’ve said, without adding that two things have happened since.  I can’t say they threw a new light; for nobody can make sense of them.  But they threw a new kind of darkness; they threw the darkness in new directions.  The first was this.  The family physician of the St. Clares quarrelled with that family, and began publishing a violent series of articles, in which he said that the late general was a religious maniac; but as far as the tale went, this seemed to mean little more than a religious man.