It was an immense, rambling stone structure situated on the top of the hill overlooking the bay, and it could be seen for miles, silhouetted against the skyline, like some ancient feudal castle. This resemblance to a castle was heightened by the fact that at each end of the mansion rose a high tower. One of these towers had been built when the mansion was first erected by Major Applegate, an eccentric old army man who had made millions by lucky real estate deals and had laid the foundation for the Applegate fortune. The mansion had been the admiration of its day, and in its time had seen much gaiety. But as the years passed the Applegate family became scattered until at last there remained but Hurd Applegate and his sister Adelia, who continued living in the vast and lonely old mansion. Hurd Applegate was a man of about sixty years of age. He was a tall, stooped man, eccentric in his ways, and his life seemed to be devoted to the collection of rare stamps. He was an authority on the subject, and nothing else in life appeared to hold a great deal of interest for him. The only visitors at Tower Mansion were philatelists from New York or experts desirous of appraising some new stamp that Hurd Applegate had managed to secure from some remote part of the world. It had often been said in Bayport that Hurd Applegate had accomplished only two things in life--he had collected stamps and he had built a new tower on the mansion. The new tower, a duplicate of the original tower at the opposite end of the great building, had been built but a few years--even well within the memory of the two Hardy boys. Adelia Applegate, who lived in the Tower Mansion with her brother, was a maiden lady of uncertain years. The records in Bayport's city hall gave her age as fifty-five, but Miss Applegate admitted it to no one. She was as eccentric as her brother, and lived very much to herself, being seldom seen in the city. She was at one time a blonde, but she had endeavored to retain her youth by dyeing her hair, with the result that it was now a sort of dusty black. Chet Morton was fond of saying that "Miss Applegate used to be a blonde but she dyed." She dressed in all colors of the rainbow, and her infrequent excursions into Bayport stores, when she would order the clerks about like so many soldiers, shouting at them in her high, cracked voice, had become historic on account of the wild and colorful garments she would carry off with her. These eccentric people were reputed to be enormously wealthy, although they lived simply and kept only a few servants. So when Hurd Applegate came into the Bayport police station that afternoon and reported that the safe in his library had been broken open and that it had been robbed of all the securities and jewels it contained, the rumors that soon spread about the city magnified the actual loss until it became common talk that the loss amounted anywhere from one hundred thousand to a million dollars.