In the novel Death in the Clouds, GF 45 is the code name given by Madame Giselle to one of her “clients” in her small black notebook. GF 45 is English and has attempted to murder someone.
Hercule Poirot and Monsieur Fournier theorised that anyone of the passengers onboard “Prometheus”, apart from Armand or Jean Dupont, could be GF 45.