The story is an engaging one, as young Canty, inspired by his mother and a local priest to dream of a finer life than his father, an ill-tempered beggar (Barton MacLane) could provide, sneaks onto the grounds of Buckingham Palace. There, he meets young Prince Edward, who is thrilled to meet a boy his own age...and, after cleaning him up a bit, is astonished to discover that the pair could pass as twins. Edward decides this is a golden opportunity to see what life outside the Palace is really like, so, against Canty's misgivings, the two exchange clothing, and the Prince leaves...creating far more of an uproar than either boy could ever imagine!

Canty is soon considered 'mad', as he insists he is not Edward, and the Prince, abused and ridiculed by Tom's father, is unceremoniously thrown off the Palace grounds when he attempts to return, by a disbelieving Captain of the Guards (Alan Hale, in the first of 12 films he'd make with his friend, Errol Flynn). The ambitious Earl of Hertford (the always brilliant Claude Rains) investigates Canty's claim, and realizes, after interviewing the Captain, that the boy is telling the truth, giving him a golden opportunity to seize power. Ordering the Captain to find and kill the Prince, the Earl then threatens to kill Canty if he doesn't obey his commands.

Things grow desperate for the young Prince, as he attempts to evade his murderous 'father' on the streets, until Miles Hendon (Flynn), a roguish but good-natured 'soldier-for-hire' comes to his aid. Offering his protection to the lad, Hendon thinks him a bit balmy, as well...until events (the child's obvious despair over the death of Henry VIII, the Palace search party, and a sword duel with the Captain, where Flynn KILLS Alan Hale!!!) convince him otherwise. Then it becomes a race against time to smuggle the real King into the Coronation, before Canty is crowned, and the Earl assumes "the Power behind the Throne".