The doctor tried to put himself in Charles's place to see how a delver would be likely to start, but could not gain much inspiration from this method. Then he decided on elimination as a policy, and went carefully over the whole subterranean surface both vertical and horizontal, trying to account for every inch separately. He was soon substantially narrowed down, and at last had nothing left but the small platform before the washtubs, which he had tried once before in vain. Now experimenting in every way possible, and exerting a double strength, he finally found that the top did indeed turn and slide horizontally on a corner pivot. Beneath it lay a trim concrete surface with an iron manhole, to which Mr. Ward at once rushed with excited zeal. The cover was not hard to lift, and the father had quite removed it when Willett noticed the queerness of his aspect. He was swaying and nodding dizzily, and in the gust of noxious air which swept up from the black pit beneath the doctor soon recognised ample cause.