"Cab," repeated Mr. Lawley, looking dubiously at me; "we want an
omnibus."

"Dr. Jervis and I can walk," Walter Hornby suggested. "We shall probably
get there as soon as you, and it doesn't matter if we don't."

"Yes, that will do," said Mr. Lawley; "you two walk down together. Now
let us go."

We trooped out on to the pavement, beside which a four-wheeler was drawn
up, and as the others were entering the cab, Thorndyke stood close
beside me for a moment.

"Don't let him pump you," he said in a low voice, without looking at me;
then he sprang into the cab and slammed the door.

"What an extraordinary affair this is," Walter Hornby remarked, after we
had been walking in silence for a minute or two; "a most ghastly
business. I must confess that I can make neither head nor tail of it."

"How is that?" I asked.

"Why, do you see, there are apparently only two possible theories of the
crime, and each of them seems to be unthinkable. On the one hand there
is Reuben, a man of the most scrupulous honour, as far as my experience
of him goes, committing a mean and sordid theft for which no motive can
be discovered--for he is not poor, nor pecuniarily embarrassed nor in
the smallest degree avaricious. On the other hand, there is this
thumb-print, which, in the opinion of the experts, is tantamount to the
evidence of an eye-witness that he did commit the theft. It is