ine in
his ears, he knew he was starting what was likely to prove a wild-goose
chase. Even if he caught Graves, he didn't know what he could do, except
that he meant to get back the papers.

More and more, as he rode on, the mystery of Graves' behavior puzzled him,
worried him. He knew that Graves had been sore and angry when he had not
been chosen for the special duty detail. But that did not seem a sufficient
reason for him to have acted as he had. He remembered, too, the one glimpse
of Graves they had caught before, in a place where he did not seem to
belong.

And then, making the mystery still deeper, and defying explanation, as it
seemed to him, was the question of how Graves had known, first of all,
where they were, and of how he had reached the place.

He had no motorcycle of his own or he would not have ridden away on Dick's
machine. He could not have come by train. Harry's head swam with the
problem that presented itself. And then, to make it worse, there was that
remark Graves had made. He had said Harry would find it hard to explain
where he had been. How did he know where they had been? Why should he think
it would be hard for them to explain their actions?

"There isn't any answer," he said to himself. "And, if there was, I'm a
juggins to be trying to find it now. I'd better keep my mind on this old
machine, or it will ditch me! I know what I've got to do, anyhow, even if I
don't know why."

Mile after mile he rode, getting the very best speed he could out of the
machine. Somewhere ahead of him, he was sure, riding back toward London,
was Graves. In this wild pursuit he was taking chances, of course. Graves
might have turned off the road almost anywhere. But if he had done that,
there was nothing to be done about it; that much was certain. He could only
keep on with the pursuit, hoping that his quarry was following the straight
road toward London. And, to be sure, there was every reason for him to
hope just that.

By this time it was very late. No one was abroad; the countryside was
asleep. Once or twice he did find someone in the streets of a village as he
swept through; then he stopped, and asked if a man on another motorcycle
had passed ahead of him. Two or three times the yokel he questioned didn't
know; twice, however, he did get a definite assurance that Graves was ahead
of him.

Somehow he never thought of the outrageously illegal speed he was making.
He knew the importance of his errand, and