Mr 420 movie story focuses on how a village boy turns Mr 420 in city and his embarrassing moments. A village boy Krishna (Ganesh) loses his grandmother and his uncle (Rangayana Raghu) takes him to the city assuring him a luxurious life.
After realising that his uncle is a petty thief, he walks out of his house but ends on the street, as all his money and clothes are stolen.
This incident makes him to change his earlier stand and decides to follow the words of his uncle. But as per his girlfriend Rukmini's (Pranitha) order, he changes again but sooner than later he lands in a big trouble. How he tries to handle the situation and comes clean form the remaining part of the story.