leave you, I will not have to tie your hands and feet. After I am gone
you may take the handkerchief off, but when you hear me rap on the
wall, ready to come back again, you must once more blindfold yourself.
Otherwise I shall have to tie you up."

Mark considered a moment. It was not pleasant to be tied with the cruel
ropes, and he felt that in time he could penetrate the mystery of how
the room opened, even if he did not see his jailer enter and leave.

"I promise," he said finally.

"That's good. It simplifies matters. Now you can blindfold yourself,
and I trust to your honor. You may remove the bandage in five minutes,
but when you hear me knock, you must replace it until I am in the
apartment. Then you can take it off again."

There was little choice but to obey, and Mark tied the handkerchief
over his eyes. He listened intently, heard the man moving about the
room, felt the wind on his cheeks, and then came silence.

He waited until he thought five minutes had passed, and then took off
the bandage. The candle was burning where the man had set it, but the
fellow himself was gone. He had taken with him the broken dishes, and
remains of the food Mark had not eaten. The glass and a pitcher of
water stood on a broken table, and Mark took a big drink.

"Now to see if I can't get out of this place," he murmured to himself.

Mark had invented many pieces of apparatus, and he was considered a
good mechanician. Consequently he went about his task in a systematic