Allan Quatermain was the quintessential Victorian English gentleman cum African big-game hunter. In this book, the second in the series, Quaterman and his two good friends from KSM have tired of their dull and unfulfilling lives in England, and decide to search for the truth of an old tale about the existence of an isolated white kingdom deep in darkest Africa. Their journey and subsequent adventures are sure to satisfy those who enjoy tales of dangerous quests and heroic just-in-time derring-do.
Allan Quatermain appears in some 15 to 18 stories or books by H. Rider Haggard. (The number varies by source and apparently depends on how one chooses to count the shorter stories.) Haggard suggests that Quatermain was the author of the works, and he (Haggard) only edited and published them. The most famous Quatermain book is the first, King Solomon's Mines (1885), and the sequel (1887) was Allan Quatermain - in which the main character, shall we say, departs for a better place! All the other Quatermain books - even those whose events occurred earlier in time - seem to have been written after these two main titles.
The internal chronology of Quatermain's life is a big mess, to be honest. As you study the research and learn of the numerous contradictions of timing of events in the books, you see that conjecture and invention are required to create any kind of internal chronology that makes sense. So my advice is to read (listen to) the books for enjoyment, don't take notes!, and don't worry about how one event simply can't be possible on the apparent date because it conflicts wtih some other event in a different story! Hey! It's fiction - anything goes!