Chief Fleck had spent a sleepless night trying to put two and two together. Instead of the answer being "four" as it should have been each time he completed his figuring the result was "zero." Time and again he mustered the facts into columns, only to succeed in puzzling himself the more.

Two German spies, the Hoffs, had set out together in their motor on their usual mysterious Wednesday mission. Two other persons, two of his most intelligent operatives, Thomas Dean and Jane Strong, had set out on a motorcycle to shadow them.

What had happened?

Otto Hoff had returned to his apartment on foot, hours before his usual time, seemingly much perturbed about something.

Frederic Hoff had arrived back at the apartment, also on foot, some hours later than usual, and the motor had not been returned to its usual garage. Frederic Hoff had appeared to be unusually elated about something.

Thomas Dean was in a doctor's home somewhere up the Hudson with a broken arm and a bad scalp wound and was unable to tell what had become of either Miss Strong or the motorcycle.

Jane Strong had arrived home in a taxicab half an hour before Frederick Hoff, apparently unhurt but in a most peculiar condition of mind. When Chief Fleck had called her on the 'phone she had refused to answer any questions. The best he could get out of her was a promise that she would come to his office in the morning.

From this situation Fleck's shrewd and experienced mind had been wholly unable to make any satisfactory deductions. That something unforeseen and unusual had happened to the Hoffs he was certain. It was the first time on a Wednesday that they had not returned together. Whatever it was that had happened it had depressed old Otto and had been a cause of elation to Frederic. What could it have been? That was the poser.

Coupled with this was the annoying fact of Jane Strong's sudden reticence. Hitherto he had found her at all times ready and eager whenever he called on her--ready to do anything he asked her, or to tell him everything. Why had she suddenly balked? He recalled that Dean had hinted, and Carter, too, that the girl was becoming interested in the younger of the Germans, yet he scouted the possibility of Jane having gone over to the enemy's side. A girl of her stock, living with her parents, with a brother fighting in France, never could be guilty of disloyalty, even if she were in love. Yet how was her disinclination to talk to be accounted for? After he had received a report that she was at home he had waited, expecting her to call him up. When she had not done so, he had called her. She had been positively curt and decisive. She had nothing to say to him, she had replied, at present. Dean was safe.