Glad I'm reading these out of order, because if this was my second Flashman, there might never have been a third — this was just a real disappointment after the brilliance of Flashy's historically-based debut, set during the First Afghan War and establishing his totally undeserved reputation for all his adventures to follow.
DISCLAIMER: I'm not a particular fan of anything set in Germany; I think all those Cold War spy stories (especially le Carré) just burned me out on the place. But that aside, this was still a demonstrably more lackluster story that suffered from two major weaknesses. First, this was the only Flashman book with no actual basis in history, in that aside from cameo appearances by Otto von Bismarck and Lola Montez, all characters, events and even settings here are all made up, which removes over half the fun of any Flashman story; i.e., seeing how he pops up Zelig-like in all the actual historical events of his time. And second, the whole story is based on one of the most overused and implausible tropes in fiction (see everyone from Anthony Hope to Mark Twain to Tom Cruise to Mickey Mouse): the perfect doppelganger, or "why, they could be twins! With a different haircut, no one could tell them apart — let's switch 'em!".
That said, Fraser even here is a great writer and Flashman is a great character; and sure, this WAS just his second story, and they can't all be home runs. Plus, Fraser introduces a few key concepts that then work for him throughout the series: Flashman's preternatural ability to quickly learn languages, which allows both he and Fraser to gloss over all future "but how did they communicate?" problems; and the unexplained time gaps in his narratives, which allow them to go back and fill in the blanks in future stories. In this case, the story begins with a brief episode in 1843, then jumps ahead four years to Flashman "returning from abroad" in 1847 to pick up the story again; Fraser later fills in this gap with the 6th and 9th books in the series, set in Singapore, Borneo, Madagascar and India — which makes it all the more remarkable that in this book Flashman notes that he had never been to either Paris or Germany before, (obviously, a man after my own heart).
Sadly, this was the only Flashman story ever turned into a movie (1975)…and it was (and still is) just AWFUL. A bad copy is available on YouTube (and nowhere else, for good reason) — but PLEASE don't watch it. Malcolm McDowell is unbelievably miscast as Flashman, although Oliver Reed and Alan Bates do their best as villains.* But it's hard to believe Fraser himself turned his own mediocre book into an even worse screenplay;** it is silly and stupid and poorly directed by Richard Lester, who was just coming off his successful "Three" and "Four Musketeers" films, and somehow produced this stinker before returning to form in 1976 with "Robin and Marian," (which coincidentally also capped the best year of Sean Connery's total career, which also included "The Man Who Would Be King" and "The Wind and the Lion").
As Fraser's books were NOT published in historical order, I recommend reading them in basically any other order than publication date, saving this one for well near the end (if you choose to read it at all). This was my 10th Flashman with only two left to go (both set in the American west — bo-ring), so let's just call this the odd man out in an otherwise great series. But as such, and especially when compared to Fraser's other works, it's still deserving of just two stars at best, especially considering there were still a number of far better stories Fraser could have given us instead, such as Flashman at either Gettysburg or Khartoum, both of which are alluded to in other stories.
* Sadly, this was just the second and last time these two legends shared the screen, after Ken Russell's 1969 "Women in Love," remembered mainly— if at all — for its nude male wrestling scene, (or so I'm told).
** So apparently Fraser's just bad at movies; as noted previously, he also wrote the ridiculous screenplay for "Octopussy," inarguably one of the very worst James Bond films.