Porto Rico is one of the most healthful climates on the American side of the world. The mean temperature in San Juan is officially a little over eighty degrees, and it never goes above ninety-five at any time. So the costume worn by Nick Carter was a business suit of light cloth, such as might be suitable for New York or Chicago in the summer.

The detective was careful in making up his face to represent a man in his sixties.

Crow’s-feet at the corners of his eyes, a deep line on either side from the nose to the corner of the mouth, and gray brows, as well as mustache and beard, made him look the part.

He topped it off by adjusting a well-made gray wig, which fitted so well that it appeared actually to grow on his head.

When he put on his broad-brimmed panama hat, so that it shaded his eyes, he was a typical Porto Rican, and nothing at all like the Nick Carter familiar to so many people in New York.

He moved about very quietly, for he did not want to disturb either of his assistants, who occupied a double-bedded room adjoining his own.

When he was ready to depart, he listened, for an instant, at the communicating door. Then, satisfied that nobody was stirring within, he went down the stairs to the office of the hotel, and out to the beautiful, verdure-scented avenue.

He had gone two blocks along the avenue on which the hotel stood, and was turning a corner, when he noticed two persons walking slowly along the other side, shadowed by the trees.

“Taking an evening stroll for their health, I reckon,” he thought.

He turned to see what had become of them when he had gone down the side street some distance. As they were not in sight, he decided that they had kept along the main avenue, to enjoy the breeze from the sea that swept gustily across the thoroughfare at intervals.