For Johnny Carter, the Chief Officer, the voyage has already begun badly; a revolution in the small Caribbean nation where the Campari lies in port; a tragedy that causes some passengers to be summoned home, while their places are taken by mysterious newcomers; and even the disappearance of a tactical nuclear missile from an area the ship had just visited.

The protagonist, John Carter, was played by Richard Harris, romantic interest Susan Beresford by Ann Turkel, and with Gordon Jackson, David Janssen and Burgess Meredith in supporting roles.

The often-referenced Caribbean island nation which had experienced a Socialist revolution some time before the plot begins, and which suffers from serious economic problems due to sanctions imposed by the US, is clearly Cuba, with its leader, "The Generalissimo", being Fidel Castro – though neither name is ever mentioned explicitly.

An older historical reference, from which the book's name derives, is to the fabulous Spanish treasure fleets of the 17th and 18th centuries, which attracted the attention of English pirates during the Golden Age of Piracy.

In the book is depicted a reversal of the historical linguistic roles, with 20th-century Spanish-speaking pirates seeking to loot a large consignment of gold ingots being secretly transported between the United States and Britain.