I thought I read this because of a review by Michael Dirda of the Wash. Post on Oppenheim's writings, but I can't find any such review online. Dirda or no, the review warned me this wasn't a literary gem. My interest was in spy novels that preceded Eric Ambler or John Buchan.
It was a competent book in the Buchan vein of competent but uninspired writing. Where it's not up to snuff with either Buchan or Ambler was in the area of thrills and suspense.
The story concerns two chaps who look alike and went to public school in jolly old England in the first decade of the 20th century. They meet in Africa more than ten years later (around 1913). One is a German hard-edged military type, and the other a formerly wealthy British wastrel. One kills the other with the intention of impersonating him as a spy. Or does he? We really don't know which one survived.
Unfortunately, it's easy to guess--it's a 50-50 proposition off the bat, and if you throw in the reader's expectations of what might make a gripping yarn, you reduce those odds considerably. Or am I too jaded?
At any rate, 90% of the book is conversations between the principal spy and his--not to spoil it, but--German masters, up to and including a meeting with Kaiser Wilhelm, who thanks him for his service. All these conversations generally include, "We'll get to that later," (and they're resumed the next morning), and also the chivalrous suggestion that although you're doing a swell job impersonating old so-and-so, we hope you're not screwing his wife. That might be too much for her delicate health. At any rate, in the climax the hero finds a half-man, half-beast who has been howling outside his wife's window for ten years, (hence her delicate health), and turns the spies over to the Secret Service, thus revealing that he wasn't really who people thought he was but the other guy all along. Not bad, but nothing there for writers of suspense. Nor much for readers, either.