Reading progress update: I've read 82%.

The 39 Steps   - John Buchan

'Nonsense!' said the official from the Admiralty. Sir Walter got up and left the room while we looked blankly at the table. He came back in ten minutes with a long face. 'I have spoken to Alloa,' he said. 'Had him out of bed—very grumpy. He went straight home after Mulross's dinner.'

I can only assume that this book may have inspired Agatha Christie's spy thrillers. It certainly would explain the unexplainable - that is, The Big Four and Passenger to Frankfurt.