But after a little he stumbled upon a piece of evidence which gave him a serious turn, and had kept him serious ever since.
On the morning of the discovery, Arthur, being in the neighbourhood of the "boot-box," thought he would have a look round.

There was no fear of his mistaking the place; he had been there before, and seen Mr Bickers come out of the sack.

Everything was pretty much as it had been left.

The sack lay in the corner where it had been thrown, and the cord, all except the piece which the baronet had secured, was there too.
On the dusty floor could clearly be perceived the place where Mr Bickers had rolled about in his uncomfortable shackles during the night, and on the ledge of the dim window which let light into the boot-box from the lobby still stood the tumbler which Arthur himself had officiously fetched an hour or two ago.
One or two things occurred to Arthur which had not previously struck him.

One was that the door of the boot-box was a very narrow one, and, closing-to by a spring, it would either have had to be held open or propped open while Mr Bickers was being hauled in by his captors.