Dread-Flame of M'Tonak by Henry Hasse

It seemed hours later when Ketrik awoke. He had tried in vain to find a way out of the smooth, _crystyte_-walled room. He had sought to loosen one of the heavy stones in the floor until, with bleeding and broken-nailed fingers, he had fallen into a sleep of sheer exhaustion.

Now, in the exact center of the room, he noticed a platter of food. He frowned, until it dawned on him that it must have been lowered from the ceiling! He glanced up, but if the entrance was there, it was tightly closed now.