In the Mahdi's Grasp, by George Manville Fenn.
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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.
An informative book, quite a long one, in a good Manville Fenn style,
which is well-known for sustained tension.
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