picious to me," said Joe.

"Does to me, too; but, as I have said before, you can't raid a man's
private castle on any such flimsy proof as that. You've got to have the
goods.

"Tell you what," he said after a moment's silence, "sometimes our
natural ears and eyes are better than all these instruments and wires.
I'm going out there to-morrow night alone and on foot."

"Might work," said Joe thoughtfully, "but whatever you do, you must be
careful."

"Careful?" said Curlie scornfully. "There are times when a fellow can't
afford to be careful. This thing's getting serious." He glanced over a
second message from the head office of his bureau. It was couched in no
gentle terms. He was told that this intruder must be caught and that at
once if he, Curlie Carson, wished to hold his position as chief of the
secret tower room station.

CHAPTER VI

A REAL DISCOVERY

Darkness found Curlie again on the edge of the Forest Preserve. This
time he was on foot and alone. Apparently he carried nothing. His right
hip pocket bulged, the handle of a flashlight protruded from his coat
pocket, that was all.

He did not pause at the spot where they had hid their car the night
before, but continued down the main road for a half mile farther. There
he plunged into the forest, to continue his journey under cover. Eleven
o'clock found him concealed in a clump of bushes in the woods that lay
opposite the millionaire's driveway.

"If they come to-night," he whispered to himself, "I'll know whether
they belong on that estate or not, and if they do I'll know who it is.
Anyway, I'll know it's one of J. Anson's folks. And we'll see if it is
a boy or the girl?"

The question interested him. He had no relish for getting a girl into
trouble, especially that frank-faced, smiling girl he had seen on
horseback.

"But the thing must stop," he told himself sternly, taking a tight grip
on something in his hip pocket.

The night was clear. He could see objects quite plainly. The trees, the
shrubbery, the stone pillars at the entrance to the driveway, stood out
in bold relief. For a time he sat staring at them in silence. At last he
closed his eyes and slept, as was his custom, all but his ears.

He was startled from this stupor by a sudden flash of light which made
its presence felt even through his eyelids.

As his eyes flew open, he found himself staring at two glowing
headlights. The next instant he had flattened himself in the grass.