Erstwhile King Rudolf of Ruritania is drugged and kidnapped the day before his coronation. His guards Sapt and Fritz happen upon Rudolf Rassendyll, an Englishman abroad, who bears an uncanny resemblance to the king, due to the king's ancestor's having fathered a child somewhere in the Rassendyll ancestry. Rudolf agrees to play the part of the king to prevent the king's brother "Black Michael" from gaining the throne. In the process he falls in love with the king's fiancee, Princess Flavia, who does not know of the deception. Eventually a rescue attempt is mounted, and the king is rescued from Duke Michael and his henchmen. The king returns to the palace and Rudolf to obscurity.
Almost the archetype of such stories, this is very much a dashing yarn for boys with a built-in bearded villain and lovely heroine. There's also a small collection of European mercenaries, a daring young henchman whom you can't help but admire, a slightly mysterious but attractive French woman, and of course the daring, witty, flesh-and-blood Englishman who becomes embroiled in things unwittingly and stays to see them through. There's a sense of humour throughout the book, starting with the very premise and continuing with some suave if violent exchanges.
If I were to pick holes in things, I would worry very slightly about the obvious continuing attachment between Rudolf and Flavia in spite of the latter's pending marriage to the King and wonder whether there was not a certain glorification of killing even in self-defence. But really, while all these are points to be considered, they're also rather beside the point when it comes to a story like this. Tim Golden is a computer programmer in London.  He is also the editor of the Good-to-Read website.