I suppose like characters in PG Wodehouse, many educated English girls yearn to break free from the bindings of the Victorian society as the world appeared to be open to them, with past explorers having blazed the trails and the availability of modern transportation such as steamers and railroads to take them beyond the horizons where thousands had gone before. Oh, and of course the proliferation of trashy adventure thrillers also helped spark off their imagination; few glamourous adventure heroines suffered from sea-sickness or the availability of dashing boyfriends always there for them.
When Anne, an orphaned English young lady, witnessed a death in the London tube, she found herself drawn into a real adventure without any clues to what she was really going after. All she had were vague clues that she had seen the "man in the brown suit", who was known to be present at two apparently unrelated deaths, one being the supposed accident at the tube, another was a strangled woman in the house belonging to an English MP Sir Eustace Pedler.
Finding herself on board a cruise to South Africa, Anne found the web of intrigue expanded to include several more persona dramatis; the events seemed to surround these people whom all appear to be totally legitimate.
Slowly, she learned that the affair was somehow related to one of the most daring diamond theft that occurred years ago, to a mysterious criminal organisation led by a shadowy mastermind known only as the Colonel, and with the luck of the British, she only got a couple of attempts on her life. Of course, just to make things a little bit more interesting, she found herself drawn to a man who personally declared he would strangle women with his bare hands.
Although the background of South Africa had certain significance to the plot, like the attitudes of most colonials of the time, the native colour and people were relegated far to the background.