He took a small portable electric light, run by a storage battery,
and, slipping on a pair of shoes and a bath robe, he left his
stateroom.

He had decided that the noise came from the storage compartment and so
made for that. The door he knew was not locked, since he had seen Mr.
Henderson go in late that afternoon, and the professor had used no
key.

Moving softly, Mark left his room and soon found himself in a
corridor, on either side of which were located the sleeping quarters
of the others. He did not want to awaken them, and, perhaps, be
laughed at for his curiosity.

To get to the storeroom Mark had to go first from the corridor into
the dining room. He soon reached the door that guarded what he thought
might be a strange secret. Trying the knob softly he found it giving
under his fingers.

"I wonder if I had better go in," he thought. "Perhaps, after all, it
was only rats, as Jack said."

But, even as he listened he again heard the odd sound coming from the
room. This determined him. He would solve the mystery if possible.

Cautiously he turned the knob. The door was slowly swinging open when
Mark was startled by a noise from behind him. He turned suddenly to
see Professor Henderson confronting him.