Mrs. Vernon\'s house was built in the shape of a letter L, the lady\'s wing containing the library and business office downstairs and private apartments on the second floor.

When Robert let himself into the house he entered the library to find out if the lady had yet returned.

Nothing was disturbed, and he was about to walk into the business office, when on looking out on the street he saw Frederic Vernon standing behind a nearby tree, watching the mansion closely.

"Hullo," cried Robert to himself. "What is he up to now?"

At first he thought to go out and hail Vernon, but quickly changed his mind.

"I\'ll get nothing out of him by questioning him," he reasoned. "It will pay far better to watch him and see what he does and where he goes."

A few minutes after our hero had discovered Vernon, he saw the spendthrift hurry swiftly for the wing of the house and try the window to the business office.

The sash was locked, but by inserting a knife blade between the upper and lower sashes he was enabled to push the catch back.

This done the lower sash was raised, and Frederic Vernon crawled into the business office as silently as a cat.

"He is up to no good," said our hero to himself. "I believe he is here to steal something."

There was a large Turkish chair handy, and Robert crouched behind this, that Frederic Vernon might not see him should he take a peep into the library.

"Don\'t seem to be anybody around," he heard Vernon mutter, as he looked into the library. "Frost must be off trying to hunt the old woman up."

Vernon tiptoed his way to Mrs. Vernon\'s desk, and, unlocking it, slid back the roller top.

The movement surprised Robert, for he had thought that only Mrs. Vernon and himself had keys to the desk.

"Perhaps he is using Mrs. Vernon\'s key," he thought.

With great rapidity Frederic Vernon went through several drawers full of papers.

"Pshaw! The papers must be in the safe," he murmured, and leaving the desk he approached the safe, which stood in a corner. Getting down on his knees he began to work at the combination.

"Thirty-five twice, twelve three times," he murmured, repeating what had once been the combination of the lock.

But Mrs. Vernon had had Robert to change the combination just before starting for England, and consequently Frederic Vernon failed to get the door open.

He fussed with the combination for a quarter of an hour, getting more angry over his failure every minute.

"Confound the luck, they must have changed it," he muttered. "I wish I dared to tackle Frost about it. But I am not quite ready for that. Perhaps I can make her give me the combination."

Robert did not hear the last words, yet he felt pretty certain that Frederic Vernon was responsible for his aunt\'s disappearance, and knew where she was.

He was half of a mind to call in a policeman, yet he was afraid that Vernon might in some manner give the officer of the law the slip.

"And if he is locked up now he may deny knowing anything about his aunt," was the boy\'s conclusion.

At last Vernon left the safe and went to the desk once more. Here he selected several papers and rammed them in his pocket. Then, without warning, he slipped out of the window again, closed the sash, and started down the street at a brisk pace.

"I\'ll follow him," said Robert to himself. "And I won\'t leave him out of sight until I\'ve found out what has become of Mrs. Vernon."

Running into the upper hallway Robert saw on a rack an old overcoat he had once worn and a slouch hat which had belonged to another inmate of the mansion.

He donned these, pulling the hat far down over his forehead, and the coat up around his neck. Then he put on a pair of blue glasses which Mrs. Vernon had used on the sea voyage to protect her eyes from the glare of the sun on the water.

Thus partially disguised, he made after Frederic Vernon, who had now reached the block below the house.

Here Vernon took a passing car and took a seat inside.

Running rapidly, Robert managed to catch the car, and took a position on the rear platform, with his back to the interior, that the young spendthrift might not see his face.

The car was one running well on toward the southern outskirts of Chicago, and Vernon re............