rooks have absolutely no regard for human life.'

"That's the way Sir Henry led off with his explanation. Of course he had
all that Scotland Yard knew about criminal groups to start him right.
It was a good deal to have the identity of the criminal agents selected
out; but I didn't see how he was going to manage to explain the mystery
from the evidence. I was wild to hear him. Mr. Meadows was quite as
interested, I thought, although he didn't say a word.

"Sir Henry nodded, as though he took the American's confirmation as a
thing that followed. 'We are at the scene,' he said, 'of one of the most
treacherous acts of all criminal drama. I mean the "doing in," as our
criminals call it, of the unprofessional accomplice. It's a regulation
piece of business with the hard-and-fast criminal organizations of the
Continent, like the Nervi of Marseilles, or the Lecca of Paris.

"'They take in a house servant, a shopkeeper's watchman, or a bank guard
to help them in some big haul. Then they lure him into some abandoned
house, under a pretense of dividing up the booty, and there put him out
of the way. That's what's happened here. It's a common plan with these
criminal groups, and clever of them. The picked-up accomplice would be
sure to let the thing out. For safety the professionals must "do him
in" at once, straight away after the big job, as a part of what the
barrister chaps call the res gestae.'

"Sir Henry went on nodding at us and drumming the palm of his hand on
the edge of the table.

"'This thing happens all the time,' he said, 'all about, where
professional criminals are at work. It accounts for a lot of mysteries
that the police cannot make head or tail of, like this one, for example.
Without our knowledge of this sinister custom, one could not begin or
end with an affair like this.

"'But it's simple when one has the cue--it's immensely simple. We
know exactly what happened and the sort of crooks that were about the
business. The barefoot prints show the Continental group. That's the
trick of Southern Europe to go in barefoot behind a man to kill him.'

"Sir Henry jarred the whole table with his big hand. The surface of the
table was covered with powdered chalk that the baronet had dusted over
it in the hope of developing criminal finger prints. Now under
the drumming of his palm the particles of white dust whirled like
microscopic elfin dancers.

"'The thing's clear as daylight,' he went on: 'One of the profes