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.

“Have you ’Limehouse Nights’?” she asked the attendant, naming the first book that came into her head.  She had a copy of the book at home, but that seemed to be the only title she could think of.

“We have several copies,” the girl in charge answered, “but I think they are all out.  I’ll look.”

As the clerk examined the shelves, Jane kept up a desultory talk with her, questioning her about various books on the shelves, all the while watching the old German out of the corner of her eye.  His back was toward her, and he seemed to be examining various books on the shelves, turning over the pages as if unable to decide what he wanted.  Curious as to what his taste in reading was, Jane endeavored to locate each book that he removed from its place, her idea being that she would later try to discover their titles.  To her amazement she found that it was invariably the third book in each shelf that he removed and examined—­the third from the end.  It did not appear to her that he was examining the contents of the pages so much as searching them as if he expected to find something there.

All at once, as she furtively watched from behind him, she heard him give a little pleased grunt and she saw him picking out from between the leaves of the book a fragment of paper, which he held concealed in his hand.  Watching closely, Jane saw him thrust this same hand into his trousers pocket, and when he brought it out she was certain that the hand was empty.  What did this curious performance mean?  What was the little slip of paper he had found in the book?  Why had he concealed it in his pocket?