There are many things that are unbelievable. Especially before breakfast, is it not? That is what one of your classics says. Six impossible things before breakfast.
And yet," said Poirot, "suppose an accident-" "Ah, no, my friend-" "From your point of view it would be regrettable, I agree. But nevertheless let us just for one moment suppose it. Then, perhaps, all these here are linked together - by death.