Peter Blood is a physician with the unfortunate luck of being in the wrong place at the wrong time. He treats a patient involved in the Monmouth Rebellion, attempting to overthrow the of King of England and gets caught up amongst the rebels. For his involvement by association he's branded a traitor and sentenced to death. His fate is commuted though when the king is persuaded to sell the prisoners into slavery for profit and thus begins the long descent for Blood who protests his innocence at every opportunity, imagining every man shares the same scruples as himself. It's only upon arriving in Port Royal and encountering Arabella Bishop and her father the governor that Blood comes to realize the permanence and inherent danger in his situation. Arabella grows attached and does her best to help him but his pride gets in the way and when given the opportunity for escape and revenge he takes it, becoming the pirate of the title.
This was the movie that really introduced Errol Flynn to the world. Before this he had only played bit parts, non-speaking and supporting roles. This was his first starring part in America and boy what an entrance it was. He was charismatic and energetic, his big smile and bright laugh lighting up the screen. And there's no doubting the chemistry between him and Olivia de Havilland, despite the lack of development for her character.
The film also stars Basil Rathbone as a rival pirate captain and there's a great 'swashbuckling' scene between the two. Rathbone was actually a recreational fencer in his free time so if a real fight had broken out he would likely have wiped the floor with Flynn.
As well the film benefits from an epic sweeping soundtrack by Erich Korngold, lending some majesty to scenes with a thinner budget. It also gives the film a fighting chance against another swashbuckler of better quality made in the same year "Mutiny on the Bounty" though the latter would beat it out for Best Picture.
One complaint would be that the film is rather feast or famine when it comes to pacing and plot. The good parts come in waves and with the film nearly three hours long it can drag at times. This leads to a lack of tension and even Flynn can't distract from this. Though the film received Academy Award nominations for Best Picture, Best Director, Best Writing and Best Sound Editing there were better naval films made in the same year which makes this feel like a diet pirate movie.