The Atlantic Ocean, the year 1659. The infamous English pirate Thomas Bartholomew Red (Walter Matthau), known as Captain Red, and his ship's teenage cabin boy Jean-Baptiste (Cris Campion), nicknamed "Frog", are lost on a raft without supplies in the ocean. Luckily, Captain Red and Frog are picked up by "Neptune", a Spanish galleon en route to Spain. Thrown into the brig, Red and Frog meet the ship's cook Boomako (Olu Jacobs), imprisoned after being accused of poisoning the "Neptune's" captain Linares (Ferdy Mayne) in a supposed attempt at stealing the golden throne, loot from the Aztec King Capatec Anahuac, that is being secretly transported in the galleon's hold. Captain Red becomes obsessed with capturing the throne for himself. Meanwhile, Frog falls in love with Maria-Dolores (Charlotte Lewis), the niece of Maracaibo's governor, who is travelling on the "Neptune" as a passenger.