Opening my pen-knife I scraped away the dirt and soon verified his conjecture that there was glass below. 'You're right!' I cried in my excitement. 'It is glass. Now let's search and see if we can find anything like a hinge, or at least some indication that the lead could be withdrawn at will.' We sought all along by the containing wall and found that the lead did not end in a flat sheet, as is usual, against the wall, but was turned over, and evidently continued below. 'It looks very much as if it was meant to roll up and be turned over like a blind on a roller below,' I said to my companion. 'I'm sure of it,' Dick replied with conviction. 'I'll tell you what we must do. We'll pull up the lead, make sure of the extent of the glass, then go below and search for the wizard's cell from the exact indication we shall then have of its whereabouts.' 'Right!' said I, 'that's the method.' We set to work, and soon had doubled back a strip of lead a foot broad from the centre till the glass ended by the bartizan on either side. We could not pull the lead right back because of the iron steps, which had evidently been inserted when the new wing was built, and now interfered with our further action. The glass was set in heavy leaded panes, which were so engrained with the grime of centuries that we could discern nothing through them. 'We must search for the wizard's cell from below,' I said. 'If we cannot discover it there we must return and break in from above.' 'Yes,' agreed Dick, 'it would be a pity to smash the roof in if we can find an entry below without causing damage.' The orientation was now easy, and as we studied the position from the parapet we could select the towelled window below which fitted best with the position of the glass roof. The curious thing was that the window was not situated in the centre, but at the side of the torn up lead. 'We'll find out the reason below,' I said, as we descended in great excitement, hastening on our quest. The room we made for was one of the disused chambers on the top storey, which we had remarked for its narrowness when we broke the window and thrust a towel through. 'There must be a secret passage,' cried Dick, as he flashed his torch upon the walls; 'we're not below the glass; we're to the right hand of it. Wherefore search the left wall.' Dick's inference seemed excellent, and full of eagerness I tapped with my knife, he with his poker, all along the western wall. 'There's a hollow here,' cried Dick, overjoyed, as his poker rang with a strange lightness. 'Let's hunt for an opening or crack, or some betraying sign.' 'Here! Look here!' he shouted. 'I believe this stone pulls out.'