viaduct. Oh, yes, if anybody _had_ left the train I
should have been bound to see them, of course."

"But you can't see out of both windows at once."

"Nobody could leave the train by the other side. The stone parapet of
the viaduct almost touches the footboard, and there's a drop of ninety
feet below that. Of course I see what you are driving at, Mr. Merrick.
Now look here. I locked Mr. Skidmore in the carriage myself, and I can
_prove_ that nobody got in before we left London. That would have been
too dangerous a game so long as the train was passing any number of
brilliantly lighted stations, and by the time we got into the open we
were going at sixty miles an hour. That speed never slackened till we
were just outside Lydmouth, and I was watching at the moment that our
pace dropped. I had my head out of the window of my van till we pulled
up by the platform. I am prepared to swear to all this if you like. Lord
knows how the thing was done, and I don't suppose anybody else ever
will."

"You are mistaken there," said Merrick drily. "Now, what puzzles you,
of course, is the manner in which the murderer left the train."

"Well, isn't that the whole mystery?"

"Not to me. That's the part I really do know. Not that I can take any
great credit to myself, because luck helped me. It was, perhaps, the
most amazing piece of luck I have ever had. It was my duty, of course,
to take no chances, and I didn't. But we'll come to that presently. Let
it suffice for the moment that I know how the murderer left the train.
What puzzles me is to know how he got on it. We can dismiss every other
passenger in the train, and we need not look for an accomplice. There
_were_ accomplices, of course, but they were not on the express. Why
didn't Mr. Skidmore travel in one of the corridor coaches?"

"He was too nervous. He always had a first-class carriage to himself. We
knew he was coming, and that was why we attached an ordinary first-class
coach to the train. We shouldn't do it for anybody, but Lord Rendelmore,
the chairman of Mr. Skidmore's bank, is also one of our directors. The
coach came in handy the other night because we had an order from a
London undertaker to bring a corpse as far as here--to Lydmouth."

"Really! You would have to have a separate carriage for that."

"Naturally, Mr. Merrick. It was sort of killing two birds with one
stone."

"I see. When did you hear about the undertaking job?"

"The same morning we heard from