we can, and the only way is to catch the fellow who's doing
it."

They had been in their hiding place nearly an hour, and were getting
exceedingly weary. Dunk shifted about, as did Andy, and it was on the
tip of the latter's tongue to suggest that they give up their plan for
the night when they heard a distant door opened cautiously.

"Listen!" whispered Andy.

"All right," assented his chum. "I hope it amounts to something."

With strained ears they listened. Now they heard steps coming along the
corridor. Curious, shuffling steps they were, not hard, honest
heel-and-toe steps--rather those of someone treading softly, as on soles
of rubber.

"It's him all right this time!" whispered Andy in Dunk's ear.

"I guess so--yes. Shall we follow him?"

"Yes. Take off your shoes."

Silently they removed them, and waited. The steps were nearer now, and a
long shadow was thrown athwart the place where Andy and Dunk were
hiding. They could not recognize it, however.

The shadow came nearer, flickering curiously as the swaying of an
electric lamp threw it in black relief on the corridor floor.

Then a figure came past the recess where the two lads were concealed.
They hardly breathed, and, peering out they beheld Mortimer Gaffington
stealing into Wright Hall.

It was only what they had expected to see, but, nevertheless, it gave
them both a shock.

Mortimer moved on. They could see now why he could walk so silently. He
had on rubbers over his shoes. The same trick used by the thief who had
entered Frank's room.

Mortimer looked all around. He stood in a listening attitude for a
moment, and then, as if satisfied that the coast was clear, started up
the stairs toward the corridor from which opened the room of Andy and
Dunk.

The two waited until he was out of sight, and then followed, making no
more noise than the thief himself. They timed their movements by his.
When he advanced they went forward, and when he stopped to listen, they
stopped also. It was like some game--a very grim sort of game, though.

There was only a dim light in the upper corridor, and, coming to a halt
where the shadows were deepest, Andy and Dunk watched. They saw Mortimer
stop before a student's door, try it and then came the faint tinkle of a
bunch of keys.

"Skeletons," whispered Dunk.

Andy nodded in assent.

The manipulation of the lock by means of a false key seemed to come easy
to Mortimer. In a moment he was inside the room. What