from his pocket and gazed some time at the shore. "I see my sentry at
his post," he remarked, "but no sign of a handkerchief."

"Suppose we go down-stream a short way and lie in wait for them," said
Jones, eagerly. We were all eager by this time, even the policemen and
stokers, who had a very vague idea of what was going forward.

"We have no right to take anything for granted," Holmes answered. "It
is certainly ten to one that they go down-stream, but we cannot be
certain. From this point we can see the entrance of the yard, and they
can hardly see us. It will be a clear night and plenty of light. We
must stay where we are. See how the folk swarm over yonder in the
gaslight."

"They are coming from work in the yard."

"Dirty-looking rascals, but I suppose every one has some little
immortal spark concealed about him. You would not think it, to look at
them. There is no a priori probability about it. A strange enigma is
man!"

"Some one calls him a soul concealed in an animal," I suggested.

"Winwood Reade is good upon the subject," said Holmes. "He remarks
that, while the individual man is an insoluble puzzle, in the aggregate
he becomes a mathematical certainty. You can, for example, never
foretell what any one man will do, but you can say with precision what
an average number will be up to. Individuals vary, but percentages
remain constant. So says the statistician. But do I see a
handkerchief? Surely there is a white flutter over yonder."

"Yes, it is your boy," I cried. "I can see him plainly."

"And there is the Aurora," exclaimed Holmes, "and going like the devil!
Full speed ahead, engineer. Make after that launch with the yellow
light. By heaven, I shall never forgive myself if she proves to have
the heels of us!"

She had slipped unseen through the yard-entrance and passed behind two
or three small craft, so that she had fairly got her speed up before we
saw her. Now she was flying down the stream, near in to the shore,
going at a tremendous rate. Jones looked gravely at her and shook his
head.

"She is very fast," he said. "I doubt if we shall catch her."

"We MUST catch her!" cried Holmes, between his teeth. "Heap it on,
stokers! Make her do all she can! If we burn the boat we must have
them!"

We were fairly after her now. The furnaces roared, and the powerful
engines whizzed and clanked, like a great metallic heart. Her sharp,
steep prow cut through the river-water and