What should she do? Vividly there flashed into her mind her chief's parting words.

"Watch everything," he had charged her. "Remember everything, report everything. No detail is too unimportant. If you see one of the Hoffs leave the house, don't merely report to me that the old man or the young man left the house about three o'clock. That won't do at all. I want to know the exact time. Was it six minutes after three or eleven minutes after three? I must know what direction he went, if he was alone, how long he was absent, where he went, what he did, to whom he talked. Here in my office I take your reports, Carter's reports, a dozen other reports, and study them together. Things that in themselves seem trifling, unimportant, of no value, coupled with other seemingly unimportant trifles sometimes develop most important evidence."

To prove his point he had told her of the seemingly innocent wireless message that an operator, listening in, had picked up, at a time when Germans were still permitted to use the wireless station on Long Island for commercial messages to the Fatherland. On the face of it, it was the mere announcement of the death of a relative with a few details. But a little later the same operator caught the same message coming from another part of the country, with the details slightly different, and still later another message of the same purport. Evidently, by comparing the messages, the United States authorities had been able to work out a code.

Remembering this, Jane decided that it was her particular duty just now to follow the old German and note everything he did. For several blocks she trailed along behind him, without arousing any suspicion on his part that he was being followed. He stopped once to light a cigarette, the girl behind him diverting suspicion by hastily turning to a shop window.

Again he stopped, this time before the display of viands in the window of a delicatessen store. Thoughtfully Jane noted the number, observing, too, that the name of the proprietor above the door was obviously Teutonic. She was half-expecting to see her quarry turn in here, but he walked on to the middle of the next block, where he entered a stationery store.

Hesitating but a second, to decide on a course of action, she followed him boldly into the store. She felt that she must ascertain just what he was doing in there. As she entered she saw that in the back part of the store was a lending library. Mr. Hoff had gone back to it and was inspecting the books displayed there. Unhesitatingly she, too, approached the book counter.