After an evening drinking with the King, Colonel Sapt, and Fritz von Tarlenheim in Black Michael's hunting lodge in the forest of Zenda, Rudolf Rassendyll awakes to find that the King has passed out and cannot be roused. It is the day of the King's coronation, and it appears that his wine was drugged the night before to prevent him from being crowned. Rassendyll may have been drugged as well, but the King drank much more than he did. The King has a history of drunkenness and unreliable behavior which makes Sapt predict that if he is not crowned on this day then he never will be:

"The whole nation’s there to meet him; half the army—ay, and Black Michael at the head. Shall we send word that the King’s drunk?"
"That he’s ill," said I, in correction.
"Ill!" echoed Sapt, with a scornful laugh. "They know his illnesses too well. He’s been 'ill' before!"

This is how Rassendyll came to be crowned in the King's place, but the plan was that this arrangement should only last for the day of the coronation. However, when they return from Strelsau, Rassendyll, Sapt, and Tarlenheim find the King has been abducted from the hunting lodge where they left him and taken to Black Michael's Castle at Zenda. There, for the majority of the novel, he remains as a prisoner while Rassendyll rules Ruritania in his place. It is the King's propensity for heavy drinking, but also his ill-founded trust in his treacherous half-brother, that leads to him becoming the prisoner of Zenda.