"We'll look in the soft earth beneath the windows," Nancy said. "Maybe the thief climbed in."

      "But Aunt Rosemary said all the windows on the first floor are kept locked," Helen objected.

      "No doubt," Nancy said. "But I think we should look for footprints just the same."

      The girls went from window to window, but there were no footprints beneath any. Finally Nancy stopped and looked thoughtfully at the ivy on the walls.

      "Do you think the thief climbed up to the second floor that way?" Helen asked her. "But there'd still be footprints on the ground."

      Nancy said that the thief could have carried a plank with him, laid it down, and stepped from the walk to the wall of the house. "Then he could have climbed up the ivy and down again, and gotten back to the walk without leaving any footprints."

      Once more Nancy went around the entire house, examining every bit of ivy which wound up from the foundation. Finally she said, "No, the thief didn't get into the house this way."

      "Well, he certainly didn't fly in," said Helen. "So how did he enter?"

      Nancy laughed. "If I could tell you that I'd have the mystery half solved."

      She said that she would like to look around the grounds of Twin Elms. "It may give us a clue as to how the thief got into the house."

      As they strolled along, Nancy kept a sharp lookout but saw nothing suspicious. At last they came to a half-crumbled brick walk laid out in an interesting crisscross pattern.

      "Where does this walk lead?" Nancy asked.

      "Well, I guess originally it went over to Riverview Manor, the next property," Helen replied. "I'll show you that mansion later. The first owner was a brother of the man who built this place."

      Helen went on to say that Riverview Manor was a duplicate of Twin Elms mansion. The two brothers had been inseparable companions, but their sons who later lived there had had a violent quarrel and had become lifelong enemies.