With the Peace of Amiens under strain and war with France under Napoléon Bonaparte imminent in May 1803, Hornblower is promoted from Lieutenant to Commander and appointed to command the sloop HMS Hotspur . While readying for sea, he hastily marries Maria, the daughter of his landlady, at the Garrison Church, Portsmouth. However, Hornblower marries her not out of love but out of pity, and is forced to exercise his acting ability to make her believe that he genuinely loves her.
Hotspur reconnoiters the approaches to the French naval base of Brest, and narrowly avoids capture when war is declared. Once the British fleet blockades Brest, Hornblower's restlessness and perfectionism prompts him to lead attacks and landing parties.
In spite of gaining a good reputation, Hornblower makes no financial profit from his activities. When Admiral William Cornwallis tries to put him in a position where he can make easy prize money by capturing a large shipment of Spanish gold, he instead takes on a stronger enemy frigate sent to warn the convoy and keeps it from accomplishing its mission. Eventually, by superior seamanship and skill, he drives it away. Hornblower rationalises that this is poetic justice, after he had earlier connived to facilitate the escape of his steward, who was facing hanging for striking a superior officer (a punishment Hornblower could not abide). It later transpires that the prize ships were claimed by the Admiralty (Droits of Admiralty), as war had not been officially declared against Spain at the time of the capture, so Hornblower would not have profited in any case.
Hornblower has a son, also named Horatio, and is recommended for promotion to Post Captain as one of the final acts of a retiring Admiral Cornwallis, a real figure outside of the Hornblower novels.