" Monsieur, if a doctor walks along the street and an accident happens, does he say, 'I have retired from my profession, I will continue my walk', when there is some one bleeding to death at his feet? If I had been already in Nice, and the police had sent to me and asked me to assist them, I should have refused. But this affair, the good God thrust it upon me. "

― Agatha Christie , The Mystery of the Blue Train (Hercule Poirot, #5)