ause if it was any other coloured sack, the case must begin over
again," said Father Brown; "but if it was a light brown sack, why, the
case is finished."

"I am pleased to hear it," said Angus with hearty irony. "It hasn't
begun, so far as I am concerned."

"You must tell us all about it," said Flambeau with a strange heavy
simplicity, like a child.

Unconsciously they were walking with quickening steps down the long
sweep of road on the other side of the high crescent, Father Brown
leading briskly, though in silence. At last he said with an almost
touching vagueness, "Well, I'm afraid you'll think it so prosy. We
always begin at the abstract end of things, and you can't begin this
story anywhere else.

"Have you ever noticed this--that people never answer what you say? They
answer what you mean--or what they think you mean. Suppose one lady says
to another in a country house, 'Is anybody staying with you?' the lady
doesn't answer 'Yes; the butler, the three footmen, the parlourmaid, and
so on,' though the parlourmaid may be in the room, or the butler behind
her chair. She says 'There is nobody staying with us,' meaning nobody of
the sort you mean. But suppose a doctor inquiring into an epidemic asks,
'Who is staying in the house?' then the lady will remember the butler,
the parlourmaid, and the rest. All language is used like that; you never
get a question answered literally, even when you get it answered truly.
When those four quite honest men said that no man had gone into the
Mansions, they did not really mean that no man had gone into them. They
meant no man whom they could suspect of being your man. A man did go
into the house, and did come out of it, but they never noticed him."

"An invisible man?" inquired Angus, raising his red eyebrows. "A
mentally invisible man," said Father Brown.

A minute or two after he resumed in the same unassuming voice, like a
man thinking his way. "Of course you can't think of such a man, until
you do think of him. That's where his cleverness comes in. But I came
to think of him through two or three little things in the tale Mr. Angus
told us. First, there was the fact that this Welkin went for long walks.
And then there was the vast lot of stamp paper on the window. And then,
most of all, there were the two things the young lady said--things that
couldn't be true. Don't get annoyed," he added hastily, noting a sudden
movement of the Scotchman's head; "she thought they were t