Almost as Jack spoke, the moon, which had been hidden behind a bank of clouds, peeped out, making the scene comparatively bright. The boys peered once more toward the bridge, and, as they did so, they saw a figure step from the shadows, stand revealed for an instant in the middle of the structure, and then, seemingly after a swift glance toward the approaching chums, the person darted off in the darkness.
"Did you see that?" cried Jack.
"Sure," assented Mark. "Guess he didn't want to wait for us. Why, he's running to beat the band!"
"Let's take after him," suggested Jack, and, nothing loath, Mark assented. The two lads broke into a run, but, as they leaped forward, the man also increased his pace, and they could hear his feet pounding out a tattoo on the hard road.
The two youths reached the bridge, and sped across it. They glanced hastily on either side, thinking possibly the man might have had some companions, but no one was in sight, and the stranger himself was now out of view around a bend in the highway.
"No use going any farther," suggested Jack, pulling up at the far side of the bridge. "There are two roads around the bend, and we couldn't tell which one he'd take. Besides, it might not be altogether safe to risk it."
Mark and Jack, on their return, told Professor Henderson and the German scientist something of their little excursion.
"But who could he have been?" asked Mr. Roumann. "Perhaps if you ask the boy who brought the note he can tell you."
"We'll do it in the morning," decided Mark.
"It's peculiar that he wanted Mark to meet him," spoke Amos Henderson.
"Have you any enemies that you know of, Mark?"