When Luke Fitzwilliam met Lavinia Pinkerton on a train to London, Miss Pinkerton had told him that there had been a series of murders in the village and that she believed Dr Humbleby would be next. The doctor was a nice person and "must be saved". However if she had told the doctor, he wouldn't believe her, so she was doing the next best thing by going to inform Scotland Yard. Lavinia Pinkerton was subsequently run down by a car before she could get to Scotland Yard. Luke was astonished to read a few days later that Dr Humbleby had died. Luke became intrigued and set out to investigate.
Luke discovered that Humbleby had died of septicaemia after a cut on the hand. Like many people who had died in the village recently, Humbleby had offended Lord Whitfield, the local "Lord of the Manor". Humbleby had opposed Whitfield on a water supply scheme (the details are not given) and in the process had spoken rather rudely to his Lordship.
Murder is Easy (1982 film)
Dr Humbleby dies off-screen sometime early in the 1982 film adaptation before Luke Williams arrives at the Wychwood. Here Dr Humbleby has the first name "Clarence". A unique plot line in this adaptation is to steadily build up suspicion on Bridget Conway as the prime suspect. The medical talents or lack of it of Dr Humbleby forms part of this build up. Major Horton tells Luke Williams that it is all Dr Humbleby's fault that Bridget's father died. Everyone could see that her father was dying Humbleby insisted he knew how to treat him. In this adaptation, his wife Jessie Humbleby is not featured, only his daughter Rose appears, in a fairly small role. Like in the original, Humbleby opposed Lord Easterfield in a water supply project.
Agatha Christie's Marple
In the 2009 ITV adaptation of Murder is Easy, Dr Humbleby is portrayed by Tim Brooke-Taylor. His first name here is "Edward" and the "John" is dropped. His portrayal here is similar to that in the original novel. The motive for killing him here is different. Here he is killed to preserve a dark secret from the past relating to Honoria Waynflete.