A various set of circumstances draws pointed attention to a farm where mushrooms are grown in specially build houses. But there is a part of this structure which is shut off, and this, along with mysterious comings and goings, a couple of murders and inactivity on the part of the police, makes Malcolm Bruce and Dr. Colin Wallace into amateur sleuths. They blunder about recklessly, thus making the work of Hugh Castle and Colonel Royston twice as difficult as it needed to be. Straussman is a wonder at disguising himself, and Professor Le Grand seems to be a sinister figure enough. The story rambles unduly but it is sufficiently interesting.