What events led Rudolf Rassendyll to act as the king of Ruritania?

Rudolf Rassendyll, an Englishman, found himself in Ruritania while on vacation and became embroiled in a political intrigue after meeting the king, Rudolf Elphberg. When the king was drugged and incapacitated by the villainous Duke Michael, Rassendyll was asked to impersonate him to prevent a coup. His resemblance to the king allowed him to step into the role, leading to a series of adventures as he navigated court politics and ultimately aimed to restore the rightful king to power.