The brothers explained where the Queen was parked, in case trouble should arise and their
friends had to go for help.
Frank and Joe approached the mill cautiously. It was dark now, but they did not use flashlights.
Though confident that the gatehouse was deserted, they did not wish to take any chances. As
they neared the building the Hardys could see that the shutters were tightly closed. Over the
sound of the wind in the trees came the rumble of the turning mill wheel.
The Hardys headed for the door. They had just mounted the steps when the rumbling sound of
the wheel ceased.
In the silence both boys looked around, perplexed.
'Seemed okay the other day.'
'Yes. But last time we were here at night the wheel stopped when we were about this distance away from it,' Frank observed.
Thoughtfully the boys stepped back from the mill entrance to a point where they could see the
wheel.
They stood peering at it through the darkness. Suddenly, with a dull rumble, it started to turn again!
Mystified, the Hardys advanced toward the gatehouse and stopped at the entrance. In a short
while the wheel stopped.
'Hm!' Joe murmured. 'Just like one of those electric-eye doors.'
'Exactly!' Frank exclaimed, snapping his fingers. 'I'll bet the wheel's not broken-it's been rigged up as a warning signal to be used at night!
When someone approaches the mill, the path of the invisible beam is broken and the wheel
stops. The lack of noise is enough for anyone inside to notice, and also, the lights would go out because the generator is powered by the wheel.'
The Hardys went on a quick search for the origin of the light beam. Frank was first to discover that it was camouflaged in the flour-barrel ivy planter. Beneath a thin covering of earth, and barely concealed, were the heavy batteries, wired in parallel, which produced the current
necessary to operate the light source for the electric eye.
The stopping and starting of the wheel was further explained when Frank found, screened by a
bushy shrub, a small post with a tiny glass mirror fastened on its side.
'That's the complete secret of the signal!' he exclaimed. 'This is one of the mirrors a photo-electric cell system would use. With several of these hidden mirrors, they've made a light-ring around the mill so an intruder from any side would break the beam. The barrel that contains
the battery power also contains the eye that completes the circuit.'
'I'll bet Markel and Docker rigged this up,' Joe said excitedly. 'Which means there must be something in the mill they want very badly to keep secret! We must find a way inside!'
The Hardys did not pull the wires off the battery connection, since they might have need of the warning system. Quietly and quickly the brothers made a circuit of the mill, trying doors and
first-floor windows, in hopes of finding one unlocked. But none was.
'We can't break in,' Joe muttered. Both boys were aware that time was precious-the men might return shortly. The young sleuths made another circle of the mill. This time they paused to stare at the huge wheel, which was turning once more.
'Look!' Joe whispered tensely, pointing to an open window-shaped space above the wheel.
'It's our only chance to get inside,' Frank stated. 'We'll try climbing up.'
The Hardys realized it would not be easy to reach the opening. Had there been a walkway on
top of the wheel, as there was in many mills, climbing it would have been relatively simple. The brothers came to a quick decision: to maneuver one of the paddles on the wheel until it was
directly below the ledge of the open space, then stop the motion. During the short interval
which took place between the stop and start of the wheel, they hoped to climb by way of the
paddles to the top and gain entrance to the mill.
Joe ran back through the beam, breaking it, while Frank clambered over a pile of rocks across
the water to the wheel. It rumbled to a stop, one paddle aligned with the open space above. By the time Joe returned, Frank had started to climb up, pulling himself from paddle to paddle by means of the metal side struts. Joe followed close behind.
The boys knew they were taking a chance in their ascent up the wet, slippery, mossy wheel.
They were sure there must be a timing-delay switch somewhere in the electric-eye circuit.
Could they beat it, or would they be tossed off into the dark rushing water?
'I believe I can get to the top paddle and reach the opening before the timer starts the wheel turning again. But can Joe?' Frank thought. 'Hurry!' he cried out to his brother.
Doggedly the two continued upward. Suddenly Joe's hand slipped on a slimy patch of moss. He
almost lost his grip, but managed to cling desperately to the edge of the paddle above his head, both feet dangling in mid-air.
'Frank!' he hissed through clenched teeth.
His brother threw his weight to the right. Holding tight with his left hand to a strut, he reached down and grasped Joe's wrist. With an aerialist's grip, Joe locked his fingers on Frank's wrist, and let go with his other hand.
Frank swung him out away from the wheel. As Joe swung himself back, he managed to regain
his footing and get a firm hold on the paddle supports.
'Whew!' said Joe. 'Thanks!'
The boys resumed the climb, spurred by the thought that the sluice gate would reopen any
second and start the wheel revolving.
Frank finally reached the top paddle. Stretching his arms upward, he barely reached the sill of the opening. The old wood was rough and splintering, but felt strong enough to hold his weight.
'Here goes!' he thought, and sprang away from the paddle.
At the same moment, with a creaking rumble, the wheel started to move!
*The Hidden Room**'>CHAPTER XVIII
The Hidden Room
WHILE Frank clung grimly to the sill, Joe, below him, knew he must act fast to avoid missing the chance to get off, and perhaps being crushed beneath the turning wheel. He leaped upward
with all his might.
Joe's fingers barely grasped the ledge, but he managed to hang onto the rough surface beside
his brother.
Then together they pulled themselves up and over the sill through the open space.
In another moment they were standing inside the second floor of the building. Rickety boards
creaked under their weight. Still not wishing to risk the use of flashlights, the Hardys peered around in the darkness.
'I think we're in the original grinding room,' Frank whispered as he discerned the outlines of two huge stone cylinders in the middle of the room.
'You're right,' said Joe. 'There's the old grain hopper.' He pointed to a chute leading down to the grinding stones.
Though many years had passed since the mill had been used to produce flour, the harsh, dry
odor of grain still lingered in the air. In two of the corners were cots and a set of crude shelves for clothes.
Suddenly the boys* hearts jumped. A loud clattering noise came from directly below. Then,
through a wide crack in the floor, shone a yellow shaft of light!
'Someone else must be here!' Joe whispered.
The Hardys stood motionless, hardly daring to breathe, waiting for another sound. Who was in
the suddenly lighted room?
