"Then there's the woman--the servant, Lena Kraus."

"She goes to the roof every Wednesday while the Hoffs are away to signal. Other days they apparently do the signalling themselves in some way we haven't caught on to yet. She always goes up about three o'clock and--"

"Suppose she comes down unexpectedly and catches you? We can't have that happen. That would put them on their guard."

"She won't surprise us. I've got a trick up my sleeve for preventing that."

"Go to it, then," said the chief, and Carter went on his way rejoicing.

Ever since he had been informed that the search of the Hoffs' apartment was to be intrusted to him Carter had been in a state of exuberant delight. He fairly revelled in jobs that required a disguise and he welcomed the opportunity it gave him and his assistants to don the uniform of employees of the electric light company. He even made a point of arriving that afternoon at the apartment house in the company's repair wagon, the vehicle having been procured through Fleck's assistance.

"There's a dangerous short circuit somewhere in the house," he announced to the superintendent's wife.

"My husband isn't here," she answered unsuspectingly. "Do you know where the switch-boards are?"

"We can find them," said Carter. "We'll start at the top floor and work down."

Always thorough in his methods of camouflage he actually did go through several apartments, making a pretense of inspecting switch-boards and wiring, all the while keeping watch for the time when old Lena went to the roof. The moment she had entered the elevator to ascend with her basket of linen, Carter and his aides were at the Hoff door. Equipped with the key Dean had manufactured they had no difficulty in entering.

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"Bob," said Carter to one of his men, "we haven't much time, and there's a lot to be done. You take the servant's room and the kitchen, and you, Williams, take the old man's quarters. I'll take care of the young man's bedroom, and we'll tackle the living room and dining room later."

Thoroughly experienced in this sort of work all three of them set at once to their tasks. Carter, standing for a moment in the doorway, surveyed Frederic Hoff's quarters, taking in all the details of the furnishings. Both the sitting room and the bedroom adjoining were equipped in military simplicity, with hardly an extra article of furniture or adornment, chairs, tables, everything of the plainest sort.

Moving first into the bedroom, Carter quickly investigated pillows and mattress, but in neither place did he find what he sought, evidence of a secret hiding place. He rummaged for a while through the drawers of two tables, carefully restoring the contents, but discovering nothing that aroused his suspicions. The books lying about on the tables and on shelves he examined one by one, noting their titles, examining their bindings for hidden pockets, holding them up by their backs and shaking the leaves. There was nothing there. Lifting the rugs and moving the furniture about he made a careful survey of the flooring, seeking to find some panel that might conceal a hiding place. Once or twice in corners he went so far as to make soundings but apparently the whole floor was intact. His search in the bath room was equally profitless, and at last he turned to the clothes press. As he opened the door an exclamation of amazement burst from his lips.