One, Two, Buckle My Shoe

First published 1940 and by Pan in 1956. Another printing in 1957. This copy is the third printing from 1975.

It was a morning Hercule Poirot was unlikely to forget. A morning when he was unable to feel superior in most ways to other men. In short, he paid a visit to Mr Morley, his dentist.
The afternoon was also memorable. Mr Morley was found shot.
Probing the antecedents of his fellow patients involved Poirot with a rich banker, a mysterious and unpleasant Greek, a wild young American who looked like a murderer, and an ex-actress with a most intriguing shoe-buckle...