Captain Sir Horatio Hornblower has retired to his country estate where he is the local squire, welcomed by his tenants and beloved by his wife and son. He is called back into service as a commodore to lead a fleet of English ships to the Baltic Sea, where he is instructed to damage French interests and, if possible, draw both Sweden and Russia into the greater Napoleonic wars on the side of England. Hornblower prosecutes his duty with zeal and, against all odds, accomplishes his orders with aplomb.

The novel is the eighth volume in a series and as such, most readers will be intimately familiar with Hornblower's many exploits and accomplishments. The novel frequently refers to these events as having happened during a prior time; thus, even for new readers, Hornblower is established as a capable and resourceful officer. He is often plagued by self doubt and almost always tortures himself with deep introspection and second-guessing his own decisions. Yet in action, he flawlessly makes the right choices at the right time and takes decisive action when such is warranted.

Hornblower is called up from the life of a country gentleman of means and given the office of commodore, leading a flotilla of English warships to the Baltic Sea. The Napoleonic wars have engulfed Europe and only England stands against the French tyrant. Sweden and Russia maintain a delicate neutrality in the face of increasing French aggression, and Hornblower is ordered to bring them into the war on the side of England. He proceeds to the Baltic with dispatch and encounters a French privateer, which shelters near a Swedish fortress. When Hornblower determines the Swedes will not eject the ship, in conformance with international law but over Napoleon's interests, he contrives to destroy it from a great distance. An outraged Napoleon orders an army into Swedish Pomerania as a reprisal; thereafter, Sweden enters the war against Napoleon.

Hornblower then proceeds to Russia, where he meets the Czar and engages him in political discussion. The Czar is convinced of England's naval power after touring Hornblower's flotilla, and sends an insulting response to Napoleon's incessant demands for concessions. Within days, Russia and France are also at war. Hornblower is then instructed to support Russia in any way possible. He takes his ships to Riga, where the Russians prepare a major defensive position. A huge French force closes on the city and a prolonged siege occurs where it seems that, eventually, the French must emerge victoriously. Hornblower consults with the local military leaders, including the Prussian defector Clausewitz, and together they lead a successful defense of Riga. Hornblower aids materially by several audacious plans that are executed with perfection. After months of siege, the French fail to take the city. Defections from the French occur constantly, and then plague and typhus sweep through the malnourished French army. The Russians counterattack and drive the French into full retreat. Hornblower meets with the rear-guard, composed of Prussian troops, and convinces them that their best interest lies with defecting from the French cause and taking up Prussian independence.

Shortly after this series of resounding successes, Hornblower becomes ill with typhus and collapses into fever. After weeks of illness, he regains himself and recuperates enough to travel home to England. There, he makes his report to the Admiralty and then quickly travels home where he meets his wife and child in a joyful reunion.