With a cry of recognition the simian started to descend the stairs, but at a noise from above he hesitated and then sprang back and out of sight.

An instant later the opening was closed and Billie was left in the darkness, except for the light of his torch.

CHAPTER XXIX.

THE MYSTERY DEEPENS.

While Billie was making his discoveries Donald and Adrian had also been busy.

When they left the house, at Donald's suggestion, they went first to the bank and told Don Esteban about the disappearance of the box and what the maid had seen. He was much disappointed until it was explained to him that they also had another clue.

"We shall spend our time in the slums," said Donald, "while our chum keeps watch at the house. We feel sure that between us we shall solve the mystery."

"I hope so," was Don Esteban's response. "Do you think I might be able to see this man Santiago?"

"I'm afraid not, sir! The doctor wants him to sleep as long as he can. We will let you know later in the day."

Leaving Don Esteban, the boys started for the plaza, intending to play the part of sightseers and visit every place in which a mountebank might reasonably expect to go. They felt certain that Strong would keep away from the more aristocratic places.

Keeping their eyes open and ever on the alert, they wandered about the streets and into many public places, but up to eleven o'clock had made no discovery. Then they entered a cantina for breakfast, purposely choosing one that was little frequented by Americans.

Seating themselves at a table in one corner where they could see without being seen, the boys ordered a hearty breakfast and then turned their attention to the others in the place.

At the table nearest them were three men of ordinary appearance, busy with their meal. Beyond them was an American soldier, who seemed to have dropped in out of curiosity. He was paying very little attention to his meal, but was eyeing a young woman who was seated behind the cash counter.

On the other side of the room, and partially hidden from our boys by the cash counter, was another man, smoking, and evidently waiting for some one. He kept his eye on the door and every once in a while glanced nervously at his watch.

"Not much going on in here," said Donald in English.

"No; but we are a little early. There may be more in before we finish our breakfast."

It was a true prediction, for within the next five minutes as many more persons entered and disposed themselves around the various tables. Then the boys' breakfast was served and for a few minutes they were more absorbed in the food than in the guests.

As Donald raised his eyes for a moment, however, he caught sight of a man talking to the one sitting back of the cash counter.

They were evidently arguing about something in an undertone and a minute later the newcomer took a seat with his back to the boys.

"Look!" was Donald's smothered exclamation, "over there by the cashier. Isn't that our man?"

Adrian raised his eyes and gazed hard at the back of the man's head.

"I could tell better if he would remove his hat. It does look like him, but he has disguised himself some way."

"Sure," laughed Donald. "That's part of his trade; but I'm dead sure it is Strong."

"What had we better do?"

"I don't know. He'll recognize us the minute he sees us. If he is keeping away from us, he will leave. If he is not, he may come over and speak to us. There is no reason why he should not, so far as he knows."

"How would it do to make ourselves visible?"

"I hardly know." Then after a pause: "I'll tell you what. As soon as we finish we'll go out, as though we did not see him, but we will be sure to make enough commotion to attract his attention.

Then we'll station ourselves where we can see him as he comes out."

"That's all right, Don; but suppose he doesn't come out?"

Donald scratched his head.

"Oh!" he exclaimed, "I knew I had a thought back of that. When he sees us, if he is not trying to avoid us, he will speak to us. If he does not speak to us, we will know there is something wrong and take immediate steps to have him arrested."

"But he may escape."

"How can he?"

"I suppose he could go out through the kitchen if he had to," was the ready reply.

"Yes, I suppose he could. We must do better than that."

"I'll tell you," said Adrian. "I'll go over and speak to that soldier in English. If it is Strong, he will hear me and will involuntarily make some move. If he wants to make himself known, he will. If he does not do so, we will simply sit here till he goes out and then shadow him."

"That sounds good. Go over and say 'Howdy' to the soldier."

Adrian arose from his seat and stepped over to the soldier.

"h.e.l.lo, partner!" was his somewhat noisy greeting. "Won't you come over to our table?"

"Why, sure, neighbor! I was just thinking that I was getting mighty lonesome."

He arose from his chair and took a seat beside Donald, who had been observing Strong closely. There could be no doubt that he had been attracted by Adrian's voice, but he gave no intimation that he knew the boys.

"Glad to see you," said Donald, without taking his eyes from his man. "Won't you have another cup of coffee?"

"Bet your life, neighbor!" Then as he lighted a fresh cigarette: "Smoke?"

"Never learned!" laughed Donald. "Seems mighty funny down here, doesn't it?"

"Sure does; but you're just as well off without it. Live here?"

"No," replied Adrian; "we were on our way home and got stuck!"

"What's the matter?" asked the soldier, with much concern. "Out of coin?"

"We haven't much; but Gen. Funston has promised to find us pa.s.sage home in a few days. Our friend saw him early this morning," this latter remark expressly for Strong's ears.

"If he told you he'd do it, he will," said the soldier. "You can bet on him every time."