This novel follows Horatio Hornblower on his tour during his first tour as captain of a Ship of the Line. Horatio Hornblower is a fictional officer in the British Royal Navy during the Napoleonic Wars, originally the protagonist of a series of novels by C. S. Forester, and later the subject of films and television programs. ... Ships of the line were 1st, 2nd, or 3rd-rated ships in the rating system of the Royal Navy. ...

Hornblower has recently completed a daring tour of duty abourd the Atropos, which was given to the King of Sicily. After his return to England, he is assigned to the Sutherland. The Sutherland is, by Hornblower's estimation, the ugliest ship of the line in the service. He is a assigned to report to Admiral Leighton, who is married to Lady Barbara Wesseley. Throughout, Hornblower is torn between his puppy-like love to Lady Barbara and his sense of duty and loyalty to his frumpy wife, Maria. His feelings for his wife are magnified with the recent loss of both of his children to smallpox. Smallpox (also known by the Latin names Variola or Variola vera) is a highly contagious viral disease unique to humans. ...

Hornblower's first orders are to follow an Indian convoy to safety off the Spanish coast. He boldly defends them from two simultaneous attacks from privateers. Since he has been plagued by a lack of crew, and forced to work with "lubbers, sheepstealers, and bigamists", he breaks admiralty regulations and presses twenty men from each vessel in the convoy, as they part ways. Fully manned, Hornblower wrecks havoc on the French-controlled Spanish coast. His notable actions include taking a French frigate by surprise, bombing a French fort, taking two more vessels as prizes, raking several thousand undefended French soldiers along a coastal road, and saving his Admiral's ship from certain ruin by towing it away from a French battery during a severe storm. This article is about the concept in naval history. ... Frigate is a name which has been used for several distinct types of warships at different times. ...

In the last battle described in the book, Hornblower has been forced to surrender following single-handedly disabling four French frigates. With most of his men killed or wounded and his ship demasted, he is forced to strike his colors.