Dr Thompson

In the novel The A.B.C. Murders, Dr Thompson is an eminent psychiatrist ( Christie uses the term "alienist") who is brought in by the police to help in tracking down the serial A.B.C. killer. He is consulted during two high level police conferences, the first to discuss the motive of the killer and the second on whether to publicise the killer's announce next target city.

Later in the story, he also comes with Chief Inspector Japp to brief Poirot about the initial police court proceedings against Alexander Bonaparte Cust. It appeared that the defence counsel had offered a defense that Cust, being an epileptic, might have committed the killings without knowing about them. Thompson said that was possible among some epileptics but is the case of Cust, this claim is totally undermined by the letters which showed premeditation and careful planning.

Dr Thompson is described as "a pleasant middle-aged man who, in spite of his learning, contented himself with homely language, avoiding the technicalities of his profession."