In the novel Death in the Clouds, Monsieur Henri is a hairdresser employed at Monsieur Antoine hairdressing establishment in Bruton Street where Jane Grey also works as a hairdressing assistant. It is hinted at that his real name is Henry.
In a two stage process, customers who came were typically given a shampoo or other preparatory treatment by assistants such as Jane or Gladys before being attended to by the hairdressers such as Henri or Georges.