"Well," said the woman a little doubtfully, "the clergymen came in about half an hour ago and bought some peppermints and talked a bit, and then went off towards the Heath. But a second after, one of them runs back into the shop and says, 'Have I left a parcel!' Well, I looked everywhere and couldn't see one; so he says, 'Never mind; but if it should turn up, please post it to this address,' and he left me the address and a shilling for my trouble. And sure enough, though I thought I'd looked everywhere, I found he'd left a brown paper parcel, so I posted it to the place he said. I can't remember the address now; it was somewhere in Westminster. But as the thing seemed so important, I thought perhaps the police had come about it."
"So they have," said Valentin shortly. "Is Hampstead Heath near here?"
"Straight on for fifteen minutes," said the woman, "and you'll come right out on the open." Valentin sprang out of the shop and began to run. The other detectives followed him at a reluctant trot.
The street they threaded was so narrow and shut in by shadows that when they came out unexpectedly into the void common and vast sky they were startled to find the evening still so light and clear. A perfect dome of peacock-green sank into gold amid the blackening trees and the dark violet distances. The glowing green tint was just deep enough to pick out in points of crystal one or two stars. All that was left of the daylight lay in a golden glitter across the edge of Hampstead and that popular hollow which is called the Vale of Health. The holiday makers who roam this region had not wholly dispersed; a few couples sat shapelessly on benches; and here and there a distant girl still shrieked in one of the swings. The glory of heaven deepened and darkened around the sublime vulgarity of man; and standing on the slope and looking across the valley, Valentin beheld the thing which he sought.
Among the black and breaking groups in that distance was one especially black which did not break—a group of two figures clerically clad. Though they seemed as small as insects, Valentin could see that one of them was much smaller than the other. Though the other had a student's stoop and an inconspicuous manner, he could see that the man was well over six feet high. He shut his teeth and went forward, whirling his stick impatiently. By the time he had substantially diminished the distance and magnified the two black figures as in a vast microscope, he had perceived something else; something which startled him, and yet which he had somehow expected. Whoever was the tall priest, there could be no doubt about the identity of the short one. It was his friend of the Harwich train, the stumpy little curé of Essex whom he had warned about his brown paper parcels.
Now, so far as this went, everything fitted in finally and rationally enough. Valentin had learned by his inquiries that morning that a Father Brown from Essex was bringing up a silver cross with sapphires, a relic of considerable value, to show some of the foreign priests at the congress. This undoubtedly was the "silver with blue stones"; and Father Brown undoubtedly was the little greenhorn in the train. Now there was nothing wonderful about the fact that what Valentin had found out Flambeau had also found out; Flambeau found out everything. Also there was nothing wonderful in the fact that when Flambeau heard of a sapphire cross he should try to steal it; that was the most natural thing in all natural history. And most certainly there was nothing wonderful about the fact that Flambeau should have it all his own way with such a silly sheep as the man with the umbrella and the parcels. He was the sort of man whom anybody could lead on a string to the North Pole; it was not surprising that an actor like Flambeau, dressed as another priest, could lead him to Hampstead Heath. So far the crime seemed clear enough; and while the detective pitied the priest for his helplessness, he almost despised Flambeau for condescending to so gullible a victim. But when Valentin thought of all that had happened in between, of all that had led him to his triumph, he racked his brains for the smallest rhyme or reason in it. What had the stealing of a blue-and-silver cross from a priest from Essex to do with chucking soup at wall paper? What had it to do with calling nuts oranges, or with paying for windows first and breaking them afterwards? He had come to the end of his chase; yet somehow he had missed the middle of it. When he failed (which was seldom), he had usually grasped the clue, but nevertheless missed the criminal. Here he had grasped the criminal, but still he could not grasp the clue.
The two figures that they followed were crawling like black flies across the huge green contour of a hill. They were evidently sunk in conversation, and perhaps did not notice where they were going; but they were certainly going to the wilder and more silent heights of the Heath. As their pursuers gained on them, the latter had to use the undignified attitudes of the deer-stalker, to crouch behind clumps of trees and even to crawl prostrate in deep grass. By these ungainly ingenuities the hunters even came close enough to the quarry to hear the murmur of the discussion, but no word could be distinguished except the word "reason" recurring frequently in a high and almost childish voice. Once over an abrupt dip of land and a dense tangle of thickets, the detectives actually lost the two figures they were following. They did not find the trail again for an agonising ten minutes, and then it led round the brow of a great dome of hill overlooking an amphitheatre of rich and desolate sunset scenery. Under a tree in this commanding yet neglected spot was an old ramshackle wooden seat. On this seat sat the two priests still in serious speech together. The gorgeous green and gold still clung to the darkening horizon; but the dome above was turning slowly from peacock-green to peacock-blue, and the stars detached themselves more and more like solid jewels. Mutely motioning to his followers, Valentin contrived to creep up behind the big branching tree, and, standing there in deathly silence, heard the words of the strange priests for the first time.
After he had listened for a minute and a half, he was gripped by a devilish doubt. Perhaps he had dragged the two English policemen to the wastes of a nocturnal heath on an errand no saner than seeking figs on its thistles. For the two priests were talking exactly like priests, piously, with learning and leisure, about the most aerial enigmas of theology. The little Essex priest spoke the more simply, with his round face turned to the strengthening stars; the other talked with his head bowed, as if he were not even worthy to look at them. But no more innocently clerical conversation could have been heard in any white Italian cloister or black Spanish cathedral.
The first he heard was the tail of one of Father Brown's sentences, which ended: "... what they really meant in the Middle Ages by the heavens being incorruptible."
The taller priest nodded his bowed head and said:
"Ah, yes, these modern infidels appeal to their reason; but who can look at those millions of worlds and not feel that there may well be wonderful universes above us where reason is utterly unreasonable?"
"No," said the other priest; "reason is always reasonable, even in the last limbo, in the lost borderland of things. I know that people charge the Church with lowering reason, but it is just the other way. Alone on earth, the Church makes reason really supreme. Alone on earth, the Church affirms that God himself is bound by reason."
The other priest raised his austere face to the spangled sky and said:
"Yet who knows if in that infinite universe——?"
"Only infinite physically," said the little priest, turning sharply in his seat, "not infinite in the sense of escaping from the laws of truth."
Valentin behind his tree was tearing his fingernails with silent fury. He seemed almost to hear the sniggers of the English detectives whom he had brought so far on a fantastic guess only to listen to the metaphysical gossip of two mild old parsons. In his impatience he lost the equally elaborate answer of the tall cleric, and when he listened again it was again Father Brown who was speaking:
"Reason and justice grip the remotest and the loneliest star. Look at those stars. Don't they look as if they were single diamonds and sapphires? Well, you can imagine any mad botany or geology you please. Think of forests of adamant with leaves of brilliants. Think the moon is a blue moon, a single elephantine sapphire. But don't fancy that all that frantic astronomy would make the smallest difference to the reason and justice of conduct. On plains of opal, under cliffs cut out of pearl, you would still find a notice-board, 'Thou shalt not steal.'"
Valentin was just in the act of rising from his rigid and crouching attitude and creeping away as softly as might be,