where the captain was standing.

"By jove!" gasped the captain, making a dash for the companion way, "I
believe you have it."

At this moment the steward came on deck.

"See here!" roared the captain, "What is the meaning of this?"

The steward smiled complacently, and said, "Why, sir, I know nothing
about the flag. I have finished my tasks in the pantry, and came on deck
for a breath of air."

The captain, debating the matter in his mind, concluded he would say no
more at that time, and turned his attention again to the others. The
steward went about his duties.

"They have quit signaling," reported Tom.

"What do you make of that other ship's continued interest in us,
captain?" asked the professor.

"I'm blessed if I know," he replied. "It's too deep for me. They have
been following us ever since we left the bay, and I'm blessed if I don't
think they are after us. But I cannot imagine for what purpose."

"I suspect," said the professor, "that they have some knowledge of the
fact that we are after a treasure."

"Oh," said the captain, "but they can't expect to keep us under
observation for a long trip like this. It would be ridiculous."

"What they want most likely is the chart. Only with its aid can anyone
locate the island or the treasure."

The captain sat for a few moments in thought. "There must have been
somebody on board getting the signals. Now who could it be?"

"One of the crew," suggested Tom.

"Quite likely," agreed the captain, "unless--"

"What?" said the professor.

"It was the steward."

"No," said the professor. "You can leave him out. He has been with me
for years."

"All the more reason," returned the captain. "He'll jolly well stand
watching. What we have got to do is to watch out, and perhaps we can
trap them."

"I think--" he added. With a sudden thought he got up and went to the
companion way, returning slowly to his seat. "I may have a clue."

"What is it?" cried Tom.

"It is only an idea, don't you know, and I won't say anything until I
work it out. You say the chart is aboard?"

"Yes."

The captain whistled softly for a minute. "Better put it away
somewhere."

"That has already been done," admitted the professor, looking at the
boys. "It is hidden away, and I don't think anyone can find it."

"Even if they could find it, how could they get away with it?" inquired
Tom.

"That's easily done," explained the captain, "when they find it."

"When!" interrupted To