Sapper 
Black Gang [PDF ebook] 

Although the First World War is over, it seems that the hostilities are not, and when Captain Hugh ’Bulldog’ Drummond discovers that a stint of bribery and blackmail is undermining England’s democratic tradition, he forms the Black Gang, bent on tracking down the perpetrators of such plots. They set a trap to lure the criminal mastermind behind these subversive attacks to England, and all is going to plan until Bulldog Drummond accepts an invitation to tea at the Ritz with a charming American clergyman and his dowdy daughter.