With a heavy heart Mark rejoined the professor and others.  He found them with their bonds removed.  But to guard against their escape several men were on watch outside the door.

“What are they doing?” asked the professor eagerly as Mark entered, and the boy told him what had taken place.

“They will ruin my ship and spoil the whole trip,” cried the old scientist.  “Oh, why did I ever go to the rescue of the scoundrels?”

“Never mind,” said Jack.  “Perhaps we may yet outwit them.”

Morning came at last.  The ship was still shooting forward at fast speed, in an easterly direction.  The sailors had learned, in their short stay aboard, where the food and stores were kept, and they lost little time in getting breakfast.  They sent same in to their captives, including a big pot of hot coffee, and, after partaking of this the professor and his friends felt better.

The mate of the Good Hope came in to help clear away the dishes.  As he passed Mark he slipped into the boy’s hand a note.

“Don’t read it until you are alone,” he said in a low voice, as he hurried from the room.

As soon as the other sailors had left, Mark glanced at the slip of paper.  It bore these words: 

  “Open when you hear three raps, then two, then three, and keep
  silent.”

“What is it?” asked Mr. Henderson.

Mark showed him the paper.

“I wonder what it means,” the boy said.

“Do you think he is a friend of ours?” the professor asked.

Mark told him of the mate’s conversation the night previous.

“I think we can trust him,” the scientist went on.  “He must intend to pay us a visit when the others are asleep.  When we hear the knocks as he specifies we must open the door and let him in.”

All that day the captives were kept in the living room.  Once or twice Mark was sent for to make some adjustment to the machinery, but the apparatus, for the most part, was automatic, and needed little attention.  The professor, as well as the others, were all impatience for the promised visit of the mate.  Still they felt he would not come until night.

In fact it was long past midnight before Mark, Jack and the professor, who were anxiously listening, heard the three raps, then two, then three more.  Mark quickly opened the door, and the mate stepped inside, holding his finger to his lips as a sign of caution.  Old Andy, Washington, Bill and Tom had fallen asleep.

“I have only time for a few words,” the mate said.  “I am closely watched.  Tony mistrusts me.  I will save you if I can.”

“Why have they repaid my kindness with such actions?” asked Mr. Henderson.

“Because they are desperate men,” replied the mate.  “They are nothing more than pirates.  They mutinied on the other ship, killed the captain and those of the crew who would not join them, and started off to seek their fortunes.  I pretended to join them to save my life, but I have only been watching for a chance to escape.