That Patsy would constantly keep their quarry in view, and without being suspected, Nick had not a doubt. Nor was he mistaken. At the end of twenty minutes the clever young driver slowed down upon approaching an uptown corner, and signaled Nick to get out. The detective alighted from the door on the side from which he had received the signal, yet the cab did not stop. Nick trotted along beside the vehicle for a rod or two, keeping it between him and the side street into which Patsy quickly signed that the hack had turned. "Fourth house on the right," he softly cried. "I saw them pull up at it just as I reached the corner, so I kept right on up the avenue. They've not gone in yet." "Good enough," replied Nick, approvingly. "Take home the traps I have left in the cab." "Sure thing. You don't want any help to-night against this push, do you?" "No, indeed. There'll be but little doing to-night, I imagine. Remember the house, however, in case I fail to show up." "You may gamble on that, sir. I have it down pat." They had now passed the upper corner of the side street, and Nick felt sure that he had not been seen leaving the cab. He darted quickly back of the vehicle and gained the sidewalk, then stole back and peered around the corner. Cervera and her companion were just mounting the steps of an imposing stone residence, entirely separate from its neighbors, and their carriage was driving rapidly away. Nick waited until the couple had entered the house, then he crossed to the gloom of a doorway on the opposite side and had a look at the dwelling. From basement to roof there was no sign of a light. Even the hall appeared to be in darkness, and Nick waited and watched for several minutes, expecting to see at least one of the rooms lighted. Not a glimmer or gleam, however, appeared from any quarter. "H'm!" he presently muttered, a little perplexed. "Either they are remaining in darkness, or else they have all of those windows heavily curtained. If the latter is the case, I must discover for what reason. "Possibly they are entirely alone in there, and have gone to some room at the rear of the house. Or maybe they have suspected an espionage, and are now watching from the gloom of one of those front windows. I'll fool them if that is so, and will also have a look at the rear of the house. There is something out of the ordinary here, that's certain." Keeping well in the gloom of the block of dwellings near by, Nick retraced his steps to the corner, then crossed the street and presently approached a paved driveway leading to a small stable at the rear of the suspected house. The high gate, composed of sharp iron pickets, was securely closed and locked; so Nick returned to an alley which he had just passed, and which ran back of a block of dwellings fronting on the avenue where he had left the cab.