A. E. W. Mason 
The Four Feathers [EPUB ebook] 

Just before sailing off to war in the Sudan, British guardsman Harry Feversham quits his regiment. He immediately receives four white feathers—symbols of cowardice—one each from his three best friends and his fiancée. To disprove this grave dishonor, Harry dons an Arabian disguise and leaves for the Sudan, where he anonymously comes to the aid of his three friends, saving each of their lives.
Having proved his bravery, Harry returns to England, hoping to regain the love and respect of his fiancée. This suspenseful tale movingly depicts a distinctive code of honor that was deeply valued and strongly promoted by the British during the height of their imperial power.