Commissaire Maubritane is approached by an old acquaintance, Pierre Sertat, who has become terrified by strange noises coming from within his locked and bolted villa, and who fears that the lives of himself, his wife, and his daughter may be in danger. He believes that two smuggling gangs have perfected a technique for passing through walls and will kill him if he divulges any information about them. Against his better judgment, Maubritane agrees...