“Oh, Auntie,” laughed Elaine, a bit nervously, however, “don’t be a kill-joy.  Suppose Craig isn’t about?  Who’s going to do this, if Walter and I don’t?”

In spite of all, we mounted and rode away.

. . . . . . .

Del Mar, still continuing his nefarious work of mining American harbors and bridges, had arrived at a scheme as soon as he returned from the attempt to get back from us the Sandy Hook plans.  Smith, who had stolen the plans from the War Department, was still at the bungalow.

Early in the morning, Del Mar had seated himself at his desk and wrote a letter.

“Here, Henry,” he directed his valet, “take this to Miss Dodge.”

As the valet went out, he wrote another note.  “Read that,” he said, handing it over to Smith.  “It’s a message I want you to take to headquarters right away.”

It was worded cryptically: 

A. A. L. N. Y.
 Closely watched.  Must act soon or all will be discovered.—­M.

Smith read the note, nodded, and put it into his pocket, as he started to the door.

“No, no,” shouted Del Mar, calling him back.  “This thing means that you’ll have to be careful in your getaway.  You’d better go out through my secret passage,” he added, pointing to the panel in the library wall.

He pressed the button on the desk and Smith left through the hidden passage.  Down it he groped and at the other end emerged.  Seeing no one around, he made his way to the road.  There seemed to be no one who looked at all suspicious on the road, either, and Smith congratulated himself on his easy escape.

On a bridge over a creek, however, as Smith approached, was one inoffensive-looking person who might have been a minister or a professor.  He was leaning on the rail in deep thought, gazing at the creek that ran beneath him, and now and then flashing a sharp glance about.

Suddenly he saw something approaching.  Instantly he dodged to the farther end of the bridge and took refuge behind a tree.  Smith walked on over the bridge, oblivious to the fact that he was watched.  No sooner had he disappeared than the inquisitive stranger emerged again from behind the tree.

It was the mysterious Professor Arnold who many times had shown a peculiar interest in the welfare of Elaine and myself.

Evidently he had recognized Del Mar’s messenger, for after watching him a moment he turned and followed.

At the railroad station, just before the train for New York pulled in, the waiting crowd was increased by one stranger.  Smith had come in and taken his place unostentatiously among them.

But if he thought he was to be lost in the little crowd, he was much mistaken.  Arnold had followed, but not so quickly that he had not had time to pick up the two policemen that the town boasted, both of whom were down at the station at the time.

“There he is,” indicated Arnold, “the fellow with the slight limp.  Bring him to my room in the St. Germain Hotel.”