"Oh, we have our own private taxi service," Penny chuckled. "At least I hope so."

Taking a circuitous route so they would not be noticed by the bridgeman, the girls went down to the river's edge. Far up the stream Penny saw the familiar rowboat drifting with the current. At her signal the small boy seized his oars and rowed toward sh.o.r.e.

"I was here at eight o'clock just as you said," he declared. "That fellow up there by the bridge offered me a dollar to take him across the river.

I turned him down."

"Good," approved Penny.

"Do you want to go across the river now?" the boy asked.

"Yes, please." Penny stepped into the boat and made room for Louise.

"Keep close to the bank until we are around the bend. Then I'll show you where to land."

"I guess you're afraid someone will see you," the boy commented.

"Not exactly afraid," corrected Penny. "But this way will be best."

The boat moved quietly along the high bank, well out of sight of those who stood by the drawbridge.

"The cops were here this morning," volunteered the boy as he pulled at the oars.

"You saw them visit the estate?" Penny questioned.

"Sure, there were four of 'em. They drove up in a police car and they made old Thornd.y.k.e let the bridge down so they could go across."

"Are the policemen at the estate now?"

"No, they left again in about an hour. What do you suppose they wanted over there?"

"Well, now, I couldn't guess," replied Penny. "Like as not they only wished to ask a few questions. Are the Kippenbergs at home?"

"I saw Mrs. Kippenberg drive away right after the police left."

"And her daughter?"

"I guess she must be still there. Anyway, she wasn't in the car."

The boat rounded the bend, and Penny pointed out a place on the opposite sh.o.r.e where she wished to land.

"Shall I wait for you?" the boy asked as the girls stepped from the craft.

"Yes, but not here," directed Penny. "You might row back to the opposite sh.o.r.e and keep watch from there. We ought to be ready to leave within at least an hour."

The roof top of the Kippenberg house could be seen towering above the tall trees. But as the two girls plunged into the bushes which grew thickly along the sh.o.r.e they lost sight of it entirely.

"I hope," said Louise uneasily, "that you know where you are going. It would be easy to lose one's self in this jungle."

"Oh, I have my directions straight. We should come out near the lily pool at any minute."

"What do you hope to gain by coming here, Penny?" Louise inquired abruptly.

"I thought I would try to talk with Miss Kippenberg again. There's an important question I forgot to ask her yesterday. Then I wanted to show you the estate, especially the lily pond."

"Is there anything unusual about it?"

"I'll let you be the judge," Penny answered. "We're almost there now."

They came in a moment to a path which made walking much easier. Penny went in advance of her chum. Suddenly she halted.

"See what is ahead, Lou! I never saw that thing before."

She stepped to one side so that Louise might see the tall stone tower which loomed up against a background of scarlet maples.

"How curious!" murmured Louise.

"This isn't the only queer thing I've found on the estate."

"What purpose could the tower have?" speculated Louise.

"Decoration, perhaps," replied Penny, moving forward again. "Or it might have been built for a prison."

"Listen, you have too many different theories about Grant Atherwald,"

laughed Louise. "Why don't you get one and stick to it?"

"My mind is always open to new possibilities and impressions."

"I'll say it is," agreed Louise. "I suppose you think Mrs. Kippenberg is keeping young Atherwald a prisoner in yonder tower?"

"Well, no, but you must admit it would make a lovely one. So romantic."

"Are you trying to kid me?" Louise demanded.

Penny smiled broadly as she stared up at the tower which rose perhaps twelve feet. Like every other building on the estate it had been built to resist the ages. High above her head a circular window had been cut in the wall and there was a heavy oaken door.

Reaching for the k.n.o.b, Penny turned it. Then she pressed her shoulder against the door and pushed with her entire strength.

"Locked!" she announced.

"Then we won't learn what is inside after all."

"Yes, we will," declared Penny. "You lift me up and I'll peep in the window."

"You only weigh a ton," complained Louise.

She obligingly raised Penny up as high as she could.

"Look fast," she panted. "What do you see?"