The Ghost Kings - H. Rider Haggard

Rachel Dove is a British missionary's daughter in the wilds of Africa. Her life is turned around when fellow teenager Richard Darrien rescues her from a flash flood; their common initials alone may clue the reader in that these two are another pair of Haggard's predestined lovers. Some years later, after not having seen Richard in the meantime, Rachel runs afoul of one of the author's patented lustful villains, Ishmael, a renegade Englishman who plots with the Zulu king to have Rachel for his own. The rest of the story you'll have to listen to discover. (Summary modified from Wikipedia)