As Nancy stood memorizing the numbers and their position in the eye, she suddenly had a creepy feeling that she was being watched. Turning toward the window Nancy caught sight of a man's head. He had bright red hair!

His face was nearly hidden by his hands which held a sketching pad and pencil. He was copying the numbers that were on the blackboard!

In a flash Nancy laid the blackboard face down on the floor and dashed to the window. The spy had vanished. When she looked down the side of the house, he was just reaching the last rung of a ladder. The man raced for the street.

Nancy ran down the stairs and out the door. She looked for a license plate on the spy's disappearing car. It had none!

"He won't get far before a traffic policeman stops him!" she said to herself. "I'll follow his car."

Quickly Nancy closed the front door of the house and sprinted to her car, parked on the street. She pulled a key from a hiding place and sped after the fleeing red-haired man. The young detective had seen him turn a corner and went that way.

A wild thought came to her. If the man was not stopped by the police, he might lead her to Ned! But by the time she reached the next corner the spy had disappeared. There was no one around for Nancy to ask where he might have gone and in a few minutes she gave up the chase.

Nancy decided she should return to the house. Ned's bedroom window was open and a ladder stood under it. Anyone could enter. Upon reaching the house, Nancy jumped from the car and hurried toward the ladder. Her attention was drawn to a large notebook lying near the bottom rung of the ladder. Could it have been dropped by the man who had started to sketch Ned's code? she wondered.

Nancy walked over and picked up the notebook. Excitedly she opened it.

CHAPTER X.

Treacherous Swamp

THE notebook which the stranger had lost was blank except for a single page. On this he had started to copy the numbers from the blackboard. Most of them were there and they had been written in the eye-shaped pattern.

"I wonder if the man who sketched this really was Crosson," Nancy mused. "Maybe he'll return for his notebook," the young detective thought. "I can notify the police to come here and pick him up, if he returns, but I needn't wait for them. The Nickersons are probably already wondering where I am."

Nancy stood deep in thought for a few moments, then she took the pencil attached to the notebook and quickly began to erase the figures. One by one she moved the numbers around so that if they were a code, it certainly was scrambled now! She closed the notebook and laid it back on the ground.

As she did this, another idea came to her. Suppose the spy was the same person who had come to her house and either released or flown the robot copter! If she found the same type of soil on the rungs of the ladder as she had on the copter's tires, it could be a clue. The young detective realized that two days or more had elapsed since the robot copter had taken off from a swampy, wooded area. During that lapse of time mud on shoes could have been scuffed off.

"Or the man might have been wearing different footwear today," she thought.

"I'll take a look, however, to be sure," Nancy decided. "Anyway, since I don't have a key to the house, I'll have to climb the ladder to get back inside and lock all the windows."

Slowly she mounted the rungs, examining each one thoroughly as she went. Every few seconds she would turn around to be sure the red-haired man had not returned and was about to pull her down with the ladder.

She reached the top safely and stared at the last rung. Evidently the stranger had balanced himself on his arches while he was sketching, and left sizable chunks of mud on the wood.

"It's that same mud with the little bits of wood in it!" she said to herself.

Nancy quickly stepped into Ned's bedroom and closed and locked the window. She now made sure that the other window in his room was fastened, then checked all the windows in the whole house.

She went back to Ned's bedroom, turned the blackboard over, and tested herself on the eye-shaped set of numbers. She was glad she had remembered everything correctly. Nancy now erased the whole design and put the blackboard in the closet.

Just then the telephone rang and Nancy went to answer it. The caller was Bess.

"Where are you?" she asked. "We're all getting worried about you."

"Don't worry any longer," Nancy replied. "I'll be over in a few minutes. There's been a little excitement here, but everything is all right now. Bye. See you."

Before leaving, Nancy stood in the living room and reflected on whether or not she had done everything she should.

"The ladder!" she thought. "I mustn't leave that in place. I wonder where the man got it."

The young detective decided to put it in the Nickersons' bas.e.m.e.nt. This accomplished, she called the police and suggested that they keep a watch on the house and nab the owner of the notebook if he returned.

Then Nancy climbed into her car and headed for the restaurant. During the drive her thoughts were on the mud she had seen across the top rung of the ladder.

"I must locate that mucky, swampy place. If Glenn Munson can take me on another flight, perhaps I can find it."

Nancy finally arrived at Flannery's restaurant, where the rest of her group was waiting to have dinner.

She sat down and then said, "I'm dreadfully sorry to be so late."

George spoke up. "Don't keep us in suspense. Tell us what held you up."

As Nancy related what had happened at the house, the others grew more and more astonished.

At the end of her recital, Bess asked, "What did you do with the notebook after you changed the numbers?"

"I left it where I found it and notified the police."

While they were eating, Nancy mentioned her plan of calling Glenn Munson and trying to find the swamp area where Ned might be a prisoner.

Mr. Nickerson had a suggestion. "I'm sure that the Emerson College library must have an excellent collection of books on the geology of this region. Perhaps you can find one that describes mud similar to what you found. In the meantime I'll call the State Forest Commission and see what I can find out."

When they reached home Nancy immediately went to see if the notebook was still there. It lay where Nancy had put it. A plainclothes policeman at once stepped from behind a tree and said no one had come for it.

"I'll wait a little longer, then take the notebook with me," he told Nancy. "I doubt that its owner will return." Nancy was inclined to agree with him.

Despite her concern, Nancy slept soundly that night. Early the next morning she telephoned Glenn and arranged to take a trip with him the following morning at ten o'clock.

"Sorry I couldn't make it today," he said. "By the way I have some information for you. Evidently the mysterious copter had a phony registration number on it. The authorities haven't been able to identify the owner of the craft. Wish I could have had better news for you. See you tomorrow."

"I'll be there promptly," Nancy promised. "Thanks a lot."

After breakfast the girls said good-by to Mr. and Mrs. Nickerson. There were a few seconds when each thought the others were going to cry, but they all braced themselves and wished the rest good luck in finding Ned.

"You're doing very well, Nancy," said Mr. Nickerson, "and I wish I could have picked up as many clues as you have."

The young detective said she hoped they would lead somewhere. She and the other girls climbed into her car and took the same route as they had the day before.

Upon reaching Emerson College, Nancy left the cousins at the fraternity house and went on to the campus library alone. She had met the reference librarian several times, so she was admitted on her own identification.

When Nancy told her what book she wanted to consult, Miss Greenleaf directed her to the proper section. For an hour Nancy buried herself in the fascinating subject of geological findings of Emerson and the surrounding area.

Her search for swampy districts was finally rewarded. There were three in different locations outside Emerson.