Spain in the mid-eighteenth century Jorge Juan is a sailor who has measured the terrestrial meridian and has just published a book on it, despite the objections of the Inquisition. Meanwhile, the Marquis de la Ensenada, Fernando VI’s foremost minister, is ready to strengthen a modern fleet capable of facing the British.

Jorge Juan travels to London as a scientist to participate in meetings of the Royal Society. He is received as an enlightened sailor, but he is there to spy on the English shipyards. He adopts a double identity: the real one and that of a bookseller who moves through the docks of the Thames and the port taverns looking to hire experts in shipbuilding to make Ensenada’s plans a reality. But, when discovered, he will have to flee London.

This story of espionage takes us on a stroll through London of the xviii: through the refined atmosphere of the Royal Society and the taverns, docks and slums. As well as through eighteenth century Madrid, still anchored in customs of the past.