Six steps down from Smythe’s landing the man in shirt sleeves was doing something with a pail.  Angus stopped to extract a promise, fortified with a prospective bribe, that he would remain in that place until the return with the detective, and would keep count of any kind of stranger coming up those stairs.  Dashing down to the front hall he then laid similar charges of vigilance on the commissionaire at the front door, from whom he learned the simplifying circumstances that there was no back door.  Not content with this, he captured the floating policeman and induced him to stand opposite the entrance and watch it; and finally paused an instant for a pennyworth of chestnuts, and an inquiry as to the probable length of the merchant’s stay in the neighbourhood.

The chestnut seller, turning up the collar of his coat, told him he should probably be moving shortly, as he thought it was going to snow.  Indeed, the evening was growing grey and bitter, but Angus, with all his eloquence, proceeded to nail the chestnut man to his post.

“Keep yourself warm on your own chestnuts,” he said earnestly.  “Eat up your whole stock; I’ll make it worth your while.  I’ll give you a sovereign if you’ll wait here till I come back, and then tell me whether any man, woman, or child has gone into that house where the commissionaire is standing.”

He then walked away smartly, with a last look at the besieged tower.

“I’ve made a ring round that room, anyhow,” he said.  “They can’t all four of them be Mr. Welkin’s accomplices.”

Lucknow Mansions were, so to speak, on a lower platform of that hill of houses, of which Himylaya Mansions might be called the peak.  Mr. Flambeau’s semi-official flat was on the ground floor, and presented in every way a marked contrast to the American machinery and cold hotel-like luxury of the flat of the Silent Service.  Flambeau, who was a friend of Angus, received him in a rococo artistic den behind his office, of which the ornaments were sabres, harquebuses, Eastern curiosities, flasks of Italian wine, savage cooking-pots, a plumy Persian cat, and a small dusty-looking Roman Catholic priest, who looked particularly out of place.

“This is my friend Father Brown,” said Flambeau.  “I’ve often wanted you to meet him.  Splendid weather, this; a little cold for Southerners like me.”

“Yes, I think it will keep clear,” said Angus, sitting down on a violet-striped Eastern ottoman.

“No,” said the priest quietly, “it has begun to snow.”

And, indeed, as he spoke, the first few flakes, foreseen by the man of chestnuts, began to drift across the darkening windowpane.