Given the question: Build a movie plot around this: who is mistaken to be Poo and arrested ? Nanki is mistaken for poo and arrested.
The answer is:
Queen Victoria sends Dick Deadeye (Victor Spinetti), a sailor, to recover the "Ultimate Secret" from two thieves, the Sorcerer (Peter Reeves) and his reptilian henchman, the Shameleon. They are trying to sell it to the Pirate King (George Cooper, sung Ian Samwell). At a military parade ("Entrance of the Peers"), Dick sees the Sorcerer speaking with the Pirate King. There, Nanki (John Newton, sung Casey Kelly) sees his evil twin brother Poo (same), who is picking pockets. Dick goes for backup to headquarters, the Hexagon ("Here's a how-dee-do"), finding the Captain (Peter Reeves) and the Major-General (Francis Ghent, sung John Baldry; "I am the very model of a modern major general").Dick then goes to the pirates' lair, "The Queen's Nose" ("Oh, better far to live and die"). There, Rose Maybud (Julia McKenzie, sung Liza Strike), the barmaid, wants to find "a man of pure evil", so she can reform him. She and Dick have a moment ("Prithee, pretty maiden"), but she loses interest, since he is good. The Sorcerer and his sidekick arrive ("My name is John Wellington Wells"). The Pirate King finalizes the deal to buy the Secret for a modest sum of pirate booty, and the Sorcerer goes to get it, followed by Dick.Dick arrives at the Sorcerer's shop and asks for a potion to make him handsome ("Sprites of earth and air") and makes a grab for the Secret, but it falls through the window into the basket of Little Buttercup (Miriam Karlin), a buxom seller of ribbons, laces and marine supplies. Poo steals the basket, and everyone chases him, including three policemen ("A policeman's lot is not a happy one"), but they mistake Nanki for Poo and arrest him. The Judge at his trial (Barry Cryer, "All hail great Judge"; "Now, Jurymen, hear my advice") flirts with Little Buttercup ("I'm called Little Buttercup"), ignores Nanki's evidence ("A wandering minstrel I" and "I swear to tell the truth" based on "When I go out of door"), sentences Nanki to 200 years in the Tower of London ("A Judge is he, and a good judge too") and leaves with...