Johnny Master (Dev Anand) is a romantic looking, well read, elderly bum, selling newspapers in a small earthquake-ravaged, but now reasonably rehabilitated township in Kutch Region of the State of Gujarat in India. And, as it were, Johnny Master had come out of the debris of the catastrophe after having been buried underneath for two days and nights.
Then in March of 2004 the Government of The Union of India declares its Parliamentary Elections. The Sarpanch (The town / Village Elder) and the residents of the Township decide to form their own political party to contest the elections and make Johnny Master their chosen Candidate for his forthright openness and honesty and his erudite educational background. They win hands down and Johnny becomes the people's elected representative in parliament. But destiny has other tasks laid out for him, besides being just a Member of Parliament. His opponents in the elections join hands and have him kidnapped tortured by their henchmen. In a very cruel and dastardly act of torture inflicted on him, Johnny Master regains his memory only to discover that he is Prem Batra, the richest Indian anywhere, and on the very day of his arrival had become a victim of the earthquake tragedy.
He declares his real self to his kidnappers, buys them over, and goes back to England as Prem Batra to realize he is also in a position to buy over the corrupt lot of politicians elected to parliament to secure a mandate to form the new government as against the two other rivals in the field of equally unscrupulous, and shifty power-hungry politicians lobbying and horse-trading out to stake their claims for the same. The parties have cobbled up a coalition Government in the making. But the upright and honest idealist-reformist Prem Batra does what is expected from an honest politician in a true democracy anywhere in the world. This forms the climax of Mr. Prime Minister.