Although the main plot does not focus here, within the story line the leit motif of self-sacrifice and unrequitted love does indeed appear. True to life (more times than not), there is no easy 'boy meets girl, boy gets girl, boy loses girl' scenario since from the start Rudolf knows very well that he is simply an imposter, even if his motives are pure. The problem is that when he steps into the shoes of the king of Ruritania (also named 'Rudolf'), he manages to fool everyone except the queen. She quickly picks up on the difference since the present king is much more attentive and caring than the real one! Their pseudo romance is short-lived, as the kingdom is restored to the rightful 'Rudolf' as quickly as possible.
Although cast in a fairytale-like setting, 'The Prisoner of Zenda' has no predictable 'happy ending.' A secondary love triangle among minor characters leads to a sword fight and murder. As for Rudolf Rassendyll, he respects the chivalric code of conduct and as a result loses everything. Even though he gains the queen's heart, he cannot claim to be her legitimate husband, nor does he even meet with her covertly as a lover. Honour and duty come before sentiment, only the king is never aware of his wife's true feelings for Rassendyll. Order is restored and life simply resumes its course, the only difference being the unspoken attachment between the Rassendyll and Queen Flavia. The red rose delivered to Rassendyll without fail every year is her only outward demonstration of sentiment.
If these elements are to be translated into a theme, it might read something like this: "The best choices in life are rarely the easiest to make, but a noble heart will act in the best interest of everyone concerned."