Renine and assisting him in his investigations.

They went upstairs accordingly, and, on the second floor, came to a landing
where they found the spiral staircase leading to the belvedere.

At the top of this was a platform in the open air, but surrounded by a
parapet over six feet high.

"There must have been battlements which have been filled in since,"
observed Prince Renine. "Look here, there were loop-holes at one time. They
may have been blocked."

"In any case," she said, "the telescope was of no use up here either and we
may as well go down again."

"I don't agree," he said. "Logic tells us that there must have been some
gap through which the country could be seen and this was the spot where the
telescope was used."

He hoisted himself by his wrists to the top of the parapet and then saw
that this point of vantage commanded the whole of the valley, including the
park, with its tall trees marking the horizon; and, beyond, a depression
in a wood surmounting a hill, at a distance of some seven or eight hundred
yards, stood another tower, squat and in ruins, covered with ivy from top
to bottom.

Renine resumed his inspection. He seemed to consider that the key to the
problem lay in the use to which the telescope was put and that the problem
would be solved if only they could discover this use.