H. Rider Haggard - Queen Sheba's Ring

A famed archeologist, an aging doctor, and a young army engineer set out across the African desert on a great adventure. Professor Higgs is in search of new archeological discoveries, Dr. Adams seeks to rescue his kidnapped son, and Captain Orme wants to forget an unhappy love affair. Maqueda, Daughter of Kings, ruler of the Abati, enlists their aid to destroy the sacred idol of a neighboring tribe with promises to help the doctor rescue his son. However, the idol is a second great sphinx, carved out of a mountain. In their quest they can expect little help from the weak and cowardly Abati. The road is fraught with danger, wild beasts, valiant enemies, and traitorous allies, but their greatest danger is a beautiful woman whom it is death to love.
— Summary by Anfinwen