A window in Merton’s mind let in that strange light of surprise in which we see for the first time things we have known all along.  He had often been to the Armstrongs’, on little police jobs of the philanthropist; and, now he came to think of it, it was in itself a depressing house.  The rooms were very high and very cold; the decoration mean and provincial; the draughty corridors were lit by electricity that was bleaker than moonlight.  And though the old man’s scarlet face and silver beard had blazed like a bonfire in each room or passage in turn, it did not leave any warmth behind it.  Doubtless this spectral discomfort in the place was partly due to the very vitality and exuberance of its owner; he needed no stoves or lamps, he would say, but carried his own warmth with him.  But when Merton recalled the other inmates, he was compelled to confess that they also were as shadows of their lord.  The moody man-servant, with his monstrous black gloves, was almost a nightmare; Royce, the secretary, was solid enough, a big bull of a man, in tweeds, with a short beard; but the straw-coloured beard was startlingly salted with grey like the tweeds, and the broad forehead was barred with premature wrinkles.  He was good-natured enough also, but it was a sad sort of good-nature, almost a heart-broken sort—­he had the general air of being some sort of failure in life.  As for Armstrong’s daughter, it was almost incredible that she was his daughter; she was so pallid in colour and sensitive in outline.  She was graceful, but there was a quiver in the very shape of her that was like the lines of an aspen.  Merton had sometimes wondered if she had learnt to quail at the crash of the passing trains.

“You see,” said Father Brown, blinking modestly, “I’m not sure that the Armstrong cheerfulness is so very cheerful—­for other people.  You say that nobody could kill such a happy old man, but I’m not sure; ne nos inducas in tentationem.  If ever I murdered somebody,” he added quite simply, “I dare say it might be an Optimist.”

“Why?” cried Merton amused.  “Do you think people dislike cheerfulness?”

“People like frequent laughter,” answered Father Brown, “but I don’t think they like a permanent smile.  Cheerfulness without humour is a very trying thing.”

They walked some way in silence along the windy grassy bank by the rail, and just as they came under the far-flung shadow of the tall Armstrong house, Father Brown said suddenly, like a man throwing away a troublesome thought rather than offering it seriously:  “Of course, drink is neither good nor bad in itself.  But I can’t help sometimes feeling that men like Armstrong want an occasional glass of wine to sadden them.”

Merton’s official superior, a grizzled and capable detective named Gilder, was standing on the green bank waiting for the coroner, talking to Patrick Royce, whose big shoulders and bristly beard and hair towered above him.  This was the more noticeable because Royce walked always with a sort of powerful stoop, and seemed to be going about his small clerical and domestic duties in a heavy and humbled style, like a buffalo drawing a go-cart.