“By all means,” he said; “let us go in at this side.”  And he led the way into the high side entrance at the top of the flight of steps.  Father Brown was mounting the first step to follow him when he felt a hand on his shoulder, and turned to behold the dark, thin figure of the doctor, his face darker yet with suspicion.

“Sir,” said the physician harshly, “you appear to know some secrets in this black business.  May I ask if you are going to keep them to yourself?”

“Why, doctor,” answered the priest, smiling quite pleasantly, “there is one very good reason why a man of my trade should keep things to himself when he is not sure of them, and that is that it is so constantly his duty to keep them to himself when he is sure of them.  But if you think I have been discourteously reticent with you or anyone, I will go to the extreme limit of my custom.  I will give you two very large hints.”

“Well, sir?” said the doctor gloomily.

“First,” said Father Brown quietly, “the thing is quite in your own province.  It is a matter of physical science.  The blacksmith is mistaken, not perhaps in saying that the blow was divine, but certainly in saying that it came by a miracle.  It was no miracle, doctor, except in so far as man is himself a miracle, with his strange and wicked and yet half-heroic heart.  The force that smashed that skull was a force well known to scientists—­ one of the most frequently debated of the laws of nature.”

The doctor, who was looking at him with frowning intentness, only said:  “And the other hint?”

“The other hint is this,” said the priest.  “Do you remember the blacksmith, though he believes in miracles, talking scornfully of the impossible fairy tale that his hammer had wings and flew half a mile across country?”

“Yes,” said the doctor, “I remember that.”

“Well,” added Father Brown, with a broad smile, “that fairy tale was the nearest thing to the real truth that has been said today.”  And with that he turned his back and stumped up the steps after the curate.

The Reverend Wilfred, who had been waiting for him, pale and impatient, as if this little delay were the last straw for his nerves, led him immediately to his favourite corner of the church, that part of the gallery closest to the carved roof and lit by the wonderful window with the angel.  The little Latin priest explored and admired everything exhaustively, talking cheerfully but in a low voice all the time.  When in the course of his investigation he found the side exit and the winding stair down which Wilfred had rushed to find his brother dead, Father Brown ran not down but up, with the agility of a monkey, and his clear voice came from an outer platform above.

“Come up here, Mr. Bohun,” he called.  “The air will do you good.”

Bohun followed him, and came out on a kind of stone gallery or balcony outside the building, from which one could see the illimitable plain in which their small hill stood, wooded away to the purple horizon and dotted with villages and farms.  Clear and square, but quite small beneath them, was the blacksmith’s yard, where the inspector still stood taking notes and the corpse still lay like a smashed fly.