But the man did not linger. Scrambling to his feet after his fall,
caused by his leap from the broken window, which he had smashed with a
sledge hammer as soon as he understood that his game was up, he raced
out of the yard. He turned long enough to shake his fist at the group
assembled around the projectile, and then leaped away, calling out some
words which they could not hear.

"Let's take after him," proposed Mark.

"Come on," seconded Jack.

"No, let him go; he's a desperate man, and you came just in time to
unmask him," said Professor Henderson. "He might harm you if you took
after him. Let him go. He has not done much damage. We can easily
replace the broken window. But I can't understand what his object was
in disguising himself as Mark. He certainly looked like you, Mark,
especially when he kept his face concealed. Why did he do it?"

"He wanted to go to the moon in my place," answered the former prisoner
of the deserted house.

"But why?" insisted Jack.

"Because, I think, he's crazy, and he didn't really know what he did
want. But he certainly had me well concealed," spoke Mark. "I'm free
now, however, and as soon as I get some decent clothes on I'll go with
you to the moon. I wouldn't want the moon people to see me dressed this
way."

"How did it happen?" asked Jack. "Tell us all about it. My! but I