Seventh in the long-running mystery series with Dr Launcelot Priestley

Sir Hector Davidson is in charge of Davidson’s Ltd, a manufacturer of chemical apparatus. To the dismay of his relatives and employees, he has more interest in his personal profit than in keeping the family business thriving. Along with harassing his secretary with inappropriate advances and firing the chief designer, he seems to be in the process of stealing valuable designs for his personal gain.

Sir Hector heads one evening to his country home, Bratton Grange, with a heavy case full of valuable plans and machine prototypes. When his chauffeur fails to arrive at the train station, he's forced to accept a lift in the back of a local man's van. But when the van arrives at Bratton Grange, Sir Hector has been stabbed and the case has vanished. Enter Dr Priestley…
>[From Classic Mystery]