“H’m!” thought Chick, as he heard Cervera move quickly away.  “Evidently there is something amiss between them, but what the dickens is it?”

Still watching, he soon saw Cervera return in her street attire, when Venner quickly gave her his arm, and they departed by the stairs leading to the stage door.

Chick immediately recalled Nick’s instructions—­that the couple should now be left to him.

CHAPTER VI.

A shot in the dark.

It was nearly eleven o’clock when Rufus Venner and Cervera, the latter enveloped in a voluminous black cloak, emerged from the stage door of the theater.

As they made their way through the paved area leading out to the side street, where a carriage was awaiting them, a sturdy, roughly clad fellow in a red wig and croppy beard suddenly slouched out of a gloomy corner near the stage stairway and followed them, with movements as stealthy and silent as those of a cat.

As the carriage containing Venner and the dancer rapidly whirled away, this rough fellow darted swiftly across the street, and approached a waiting cab, the door of which stood open.

“After them, Patsy!” he softly cried, as he sprang in and closed the door.

The driver of the cab was one of Nick Carter’s youthful yet exceedingly clever assistants, and the rough fellow was Nick himself.

He had left the theater the moment Cervera concluded her performance, and since had completed a perfect disguise in the cab, which he had had in waiting, with all the properties for effecting the change mentioned.

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.