In the Mahdi's Grasp

A young army officer has been captured during the wars in Soudan, and is being held as a slave in the stronghold of the Mahdi. For years it had been thought that he was dead. His friends in London decide to go and try to rescue him. One of them is a well-known and proficient surgeon. They arrive in Cairo, and proceed on down into the Soudan, where they get in contact with an influential Sheikh. They establish themselves by doing many cures, where it is possible, and gradually work themselves nearer and nearer to the place where they estimate the missing Harry to be. Eventually they are able to make contact. Harry breaks his own arm in order to be brought to the surgeon, or Hakim, for a cure. Eventually they are able to escape with him, but to do so they have to run right through a battle. They had brought out with them a personal manservant, at his own request, and he had been in a semi-disguise, by staining the skin a very deep colour. This very nearly results in his being killed on the battlefield through which they are escaping. According to Wikipedia: "George Manville Fenn (January 3, 1831, Pimlico - August 26, 1909, Isleworth) was a British writer. He worked as a teacher in Lincolnshire, until he became printer, editor and publisher of various magazines. He had eight children with his wife Susanna Leake, whom he had married in 1855. Most of his work consists of adventure stories for young readers, featuring Explorers, Smugglers, young Adventurers and Seamen. His adult novels offer critical social commentary on Victorian England, especially reconsidering economic questions."