“Proof!” he cried. “Good God! the man is looking for proof! Why, of course, the chances are twenty to one that it has nothing to do with them. But what else can we do? Don't you see we must either follow any possibility or else go home to bed?” He went into the restaurant, followed by his companions, and they were soon seated at a late luncheon at a little table, and looked at the smashed glass from the inside. Not that it was very informative to them even then.

“Got your window broken, I see,” said Valentin to the waiter as he paid the bill.

“Yes, sir,” answered the attendant, bending busily over the change, to which Valentin silently added an enormous tip. The waiter straightened himself with unmistakable enthusiasm.

“Ah, yes, sir,” he said. “Very odd thing, that, sir.”

“Indeed?” Tell us about it,” said the detective with careless curiosity.

“Well, two gents in black came in,” said the waiter; “two of those foreign parsons that are running about. They had a cheap and quiet little lunch, and one of them paid for it and went out. The other was just going out to join him when I looked at my change again and found he'd paid me more than three times too much. 'Here^[22][23],' I says to the chap who was nearly out of the door, 'you've paid too much.' 'Oh,' he says, 'have we?' 'Yes,' I says, and picks up the bill to show him. Well, that was a knock-out.”

“What do you mean?” asked the detective.

“Well, I'd have sworn on seven Bibles that I'd put 4s.2 on that bill. But now I saw I'd put 14s.”

“Well?” cried Valentin, “and then?”

“ The parson at the door he says quietly, 'Sorry to confuse your accounts, but it'll pay for the window.' 'What window?' I says. 'The one I'm going to break,' he says, and smashed that window with his umbrella.”

All three men made an exclamation; and the inspector said under his breath^[24], “Are we after escaped lunatics^[25]?” The waiter went on with his story:

“I was so knocked silly for a second, I couldn't do anything. The man marched out of the place and joined his friend just round the corner. Then they went so quick up Bullock Street that I couldn't catch them.”

“Bullock Street,” said the detective, and ran up that thoroughfare as quickly as the strange couple he pursued.

Their journey now took them through a bare brick district; streets with few lights and even with few windows. Dusk was deepening, and it was not easy even for the London policemen to guess in what exact direction they were going. Abruptly one gas-lit window broke the blue twilight; and Valentin stopped before a little sweetstuff shop. After an instant's hesitation he went in and bought thirteen chocolate cigars. He was clearly preparing an opening; but he did not need one.

An elderly woman in the shop had regarded his elegant appearance with an automatic inquiry; but when she saw the door behind him blocked with the blue uniform of the inspector, her eyes seemed to wake up.

“Oh,” she said, “if you've come about that parcel, I've sent it off already.”

“Parcel?” repeated Valentin; and it was his turn to look inquiring.

“I mean the parcel the gentleman left – the clergyman gentleman.”

“For goodness' sake,” said Valentin, leaning forward eagerly, “for Heaven's sake tell us what happened exactly.”

“Well,” said the woman, “the clergymen came in about half an hour ago and bought some peppermints and talked a bit, and then went off towards the Heath^[26]. 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 reluctantly.

The street they took was so narrow and shut in by shadows that when they came out unexpectedly into the open space under a vast sky they were startled to find the evening still so light and clear. The holiday makers who roam this region had not wholly dispersed; a few couples sat on benches; and here and there a distant girl still shrieked in one of the swings. Standing on the slope and looking across the beautiful valley, Valentin noticed the thing which he sought.

Among the black groups in the distance was one especially black – 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 unremarkable manner, he could see that the man was well over six feet high. By the time he had substantially cut the distance, he had seen something else; something which surprised 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 little cure of Essex whom he had warned about his brown paper parcels.

Now, 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. Also there was nothing wonderful in the fact that when Flambeau heard of a sapphire cross he should try to steal it. And most certainly there was nothing wonderful about the fact that Flambeau should have it all his own way^[27] 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^[28] 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 cheating so gullible a victim. But when Valentin thought of all that had happened in between, he racked his brains for the smallest rhyme or reason in it^[29]. What had the stealing of a blue-and-silver cross from a priest from Essex to do with throwing 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.

The two figures that they followed were crawling like black flies across the huge green contour of a hill. They were evidently engaged 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 hide behind clumps of trees and even to crawl in deep grass. The hunters even came close enough to hear the murmur of the discussion, but no word could be heard except the word “reason” said frequently in a high and almost childish voice. Once the detectives actually lost the two figures they were following. They did not find the trail again for an agonizing ten minutes. Under a tree in a neglected spot there was an old wooden seat. On this seat sat the two priests still in serious speech together. The gorgeous green and gold of the scenery looked beautiful on the darkening horizon; and the stars looked like solid jewels. Silently motioning to his followers, Valentin managed to hide 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 taken by doubt. Perhaps he had dragged the two English policemen to the heath in vain. For the two priests were talking exactly like priests, piously, about the problems of theology. The little Essex priest spoke more simply, with his round face turned to the stars; the other talked with his head bowed. But so innocent a clerical conversation could have been heard in any Italian cloister or Spanish cathedral.

Valentin behind his tree was biting his fingernails with silent fury. He seemed almost to hear the sniggers of the English detectives whom he had brought so far only to listen to the metaphysical gossip of two old parsons.

Father Brown was speaking:

“Look at those stars. Don't they look as if they were single diamonds and sapphires? Think of forests of adamant with leaves of brilliants. Think the moon is a blue moon, a single sapphire. But don't fancy that all that 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^[30].'”

Valentin was just in the act of rising from his rigid and crouching attitude and creeping away as softly as might be. But something in the very silence of the tall priest made him stop until the latter spoke. When at last he did speak, he said simply, his head bowed and his hands on his knees:

“Well, I think that other worlds may perhaps rise higher than our reason. The mystery of heaven is unknowable, and I can only bow my head.”

Then, without changing his attitude or voice, he added:

“Just hand over that sapphire cross of yours, will you? We're all alone here, and I could pull you to pieces like a straw doll^[31].”

The unaltered voice and attitude added a strange violence to that shocking change of speech. But the guarder of the relic only seemed to turn his head a bit. He seemed still to have a somewhat foolish face turned to the stars. Perhaps he had not understood. Or, perhaps, he had understood and sat still with terror.

“Yes,” said the tall priest, in the same low voice, “yes, I am Flambeau.”

Then, after a pause, he said:

“Come, will you give me that cross?”

“No,” said the other, and it sounded odd.

The great robber suddenly leaned back in his seat and laughed low^[32] but long.

“No,” he cried, “you won't give it me, you proud prelate. You won't give it me, you little celibate simpleton. Shall I tell you why you won't give it me? Because I've got it already in my own breast-pocket.”

The small man from Essex turned his face in the dusk, and said timidly:

“Are – are you sure?”

Flambeau yelled with delight.

“Yes, you turnip^[33]”, he cried. “I am quite sure. I had the sense to make a duplicate of the right parcel, and now, my friend, you've got the duplicate and I've got the jewels. An old dodge^[34], Father Brown – a very old dodge.”

“Yes,” said Father Brown, and passed his hand through his hair quietly. “Yes, I've heard of it before.”

Flambeau leaned over to the little priest with a sort of sudden interest.

“You have heard of it?” he asked. “Where have you heard of it?”

“Well, I mustn't tell you his name, of course,” said the little man simply. “He was a penitent, you know. He had lived prosperously for about twenty years entirely on duplicate brown paper parcels. And so, you see, when I began to suspect you, I thought of this poor chap's way of doing it at once.”

“Began to suspect me?” repeated the thief. “Did you really have the gumption to suspect me just because I brought you up to this bare part of the heath?”

“No, no,” said Brown with an air of apology. “You see, I suspected you when we first met. It's that little bulge up the sleeve where you people have the spiked bracelet.”

“How did you ever hear of the spiked bracelet?” cried Flambeau.

“Oh, one's little flock, you know!” said Father Brown, arching his eyebrows. “When I was a curate in Hartlepool, there were three of them with spiked bracelets. So, as I suspected you from the first, don't you see, I made sure that the cross should go safe, anyhow. I'm afraid I watched you, you know. So at last I saw you change the parcels. Then, don't you see, I changed them back again. And then I left the right one behind.”

“Left it behind?” repeated Flambeau, and for the first time there was another note in his voice beside his triumph.

“Well, it was like this,” said the little priest. “I went back to that sweet-shop and asked if I'd left a parcel, and gave them a particular address if it turned up. Well, I knew I hadn't; but when I went away again I did. So, instead of running after me with that valuable parcel, they have sent it to a friend of mine in Westminster.” Then he added rather sadly: “I learnt that, too, from a poor fellow in Hartlepool. He used to do it with handbags he stole at railway stations, but he's in a monastery now. Oh, one gets to know, you know^[35],” he added, rubbing his head again with the same sort of apology. “We can't help being priests^[36]. People come and tell us these things.”

Flambeau tore a brown-paper parcel out of his inner pocket. There was nothing but paper and sticks of lead inside it. He sprang to his feet, and cried:

“I don't believe you. I don't believe a bumpkin like you could manage all that. I believe you've still got the stuff on you, and if you don't give it up – why, we're all alone, and I'll take it by force!”

“No,” said Father Brown simply, and stood up also, “you won't take it by force. First, because I really haven't still got it. And, second, because we are not alone.”

Flambeau stopped in his stride forward.

“Behind that tree,” said Father Brown, pointing, “are two strong policemen and the greatest detective alive. How did they come here, do you ask? Why, I brought them, of course! How did I do it? Why, I'll tell you if you like! Lord bless you, we have to know twenty such things when we work among the criminal classes! Well, I wasn't sure you were a thief, and you really might be one of our own clergy. So I just tested you to see if anything would make you show yourself. A man generally makes a small scene if he finds salt in his coffee; if he doesn't, he has some reason for keeping quiet. I changed the salt and sugar, and you kept quiet. A man generally objects if his bill is three times too big. If he pays it, he has some motive for passing unnoticed. I altered your bill, and you paid it.”

The world seemed waiting for Flambeau to leap like a tiger. But he was stunned with curiosity.

“Well,” went on Father Brown, “as you wouldn't leave any tracks for the police, of course somebody had to. At every place we went to, I took care to do something that would get us talked about for the rest of the day. I didn't do much harm – a splashed wall, spilt apples, a broken window; but I saved the cross, as the cross will always be saved. It is at Westminster by now.

“How do you know all these tricks?” asked Flambeau.

The shadow of a smile crossed the round, simple face of his clerical opponent.

“Oh, by being a celibate simpleton, I suppose,” he said. “Has it never occurred to you that a man who does next to nothing but hear men's real sins^[37] is likely to be wholly aware of human evil? But, as a matter of fact, another part of my trade, too, made me sure you weren't a priest.”

“What?” asked the thief.

“You attacked reason,” said Father Brown. “It's bad theology.”

And even as he turned away to collect his property, the three policemen came out from under the twilight trees. Flambeau was an artist and a sportsman. He stepped back and swept Valentin a great bow^[38].

“Do not bow to me, mon ami^[39]” said Valentin. “Let us both bow to our master.”

And they both stood an instant uncovered^[40] while the little Essex priest blinked about for his umbrella.