"This tape," he explained, a few minutes later, "is operated something along the lines of a seismograph or any other instrument for detecting change in direction. An inked needle marks these straight lines and curves all the time the machine is moving, and when it is standing still it oscillates slightly. By glancing at these tapes we can tell when any chauffeur is holding out on us, for it forms a clear record--not only of the distance the machine has traveled, but of the route it followed." "Doesn't the speedometer give you the distance?" asked Whitney. "Theoretically, yes. But it's a very simple matter to disconnect a speedometer, while this record is kept in a locked box and not one driver in ten even knows it's there. Now, let's see what Murphy's record tape tells us.... "Yes, here's the trip to the theater around eight-thirty. See the sharp turn from Fifth Avenue into Forty-second Street, the momentary stop in front of the Amsterdam, and the complete sweep as he turned around to get back to Broadway. Then there's the journey up to the Bronx or Harlem or wherever he went, another complete turn and an uninterrupted trip back down on Broadway." "Then this," cut in Whitney, unable to keep the excitement out of his voice, "is where he stopped to speak to the Germans?" "Precisely," agreed the other, "and, as you'll note, that stop was evidently longer than either of the other two. They paid their fares, while Murphy's friends had to be relieved of two hundred and fifty dollars." "From there on is what I'm interested in," announced Whitney. "What does the tape say?" "It doesn't _say_ anything," admitted the manager, with a smile. "But it _indicates_ a whole lot. In fact, it blazes a blood-red trail that you ought to be able to follow with very little difficulty. See, when the machine started it kept on down Broadway--in fact, there's no sign of a turn for several blocks." "How many?" "That we can't tell--now. But we can figure it up very accurately later. The machine then turned to the right and went west for a short distance only--stopped for a few moments--and then went on, evidently toward the ferry, for here's a delay to get on board, here's a wavy line evidently made by the motion of the boat when the hand ought to have been practically at rest, and here's where they picked up the trip to Trenton. Evidently they didn't have to stop until they got there, because we have yards of tape before we reach a stop point, and then the paper is worn completely through by the action of the needle in oscillating, indicative of a long period of inaction. The return trip is just as plain." "But," Whitney objected, "the whole thing hinges on where they went before going to Trenton. Murphy said they didn't have any bags, so they must have gone home or to some rendezvous to collect them. How are we going to find the corner where the machine turned?"