Beau Geste

Beau Geste is a 1924 adventure novel by P. C. Wren. It has been adapted for the screen several times.

Michael "Beau" Geste is the protagonist. The main narrator (among others), by contrast, is his younger brother John. The three Geste brothers are a metaphor for the British upper class values of a time gone by, and "the decent thing to do" is, in fact, the leitmotif of the novel. The Geste brothers are orphans and have been brought up by their aunt at Brandon Abbas. The rest of Beau's band are mainly Isobel and Claudia (only daughter of Lady Patricia, and in a way, also reason enough for Michael to join the French Foreign Legion), and Lady Patricia's relative Augustus (always considered "the heir" of Sir Hector Brandon). When a precious jewel known as the "Blue Water" goes missing, suspicion falls on the young people, and Beau leaves Britain to join the Foreign Legion (la Légion étrangère), followed by his brothers, Digby (his twin) and John. 

The original novel, on which the various films are more or less loosely based, provides a detailed and fairly authentic description of life in the pre-1914 Foreign Legion, which has led to (unproven) suggestions that P. C. Wren himself served with the legion.