The Pit Prop Syndicate of Freeman Wills Crofts

An Anglo-Irish mystery author during the Golden Age of Detective Fiction. 

Another brilliantly ingenious detective story by the author of The Ponson Case. The mystery of the real business of the syndicate utterly baffled the clever young "amateurs" who tried to solve it, and it took all the experience and perseverance of the "professionals" to break up the dangerous and murderous gang.