Sir Edward Pellew visits Horatio Hornblower who is jail in Jamaica awaiting his trial on a charge of making a mutiny. His problems began six months earlier when he was appointed Third Lieutenant aboard the HMS Renown under the famous Captain James Sawyer. It soon becomes apparent to several of the officers, including Horatio's friend Archie Kennedy who is aboard ship as Fourth Lieutenant that the Captain is suffering from madness of some sort. He is cruel and sees conspiracies everywhere. Both Horatio and Midshipman Welland prove to be the particular objects of his wrath. The situation is not helped by an inexperience First Lieutenant who does not command the Captain's respect and a newly arrived Second Lieutenant who doesn't seem ready to challenge the Captain in any way.

Before taking the Renown back to Jamaica for their court martial on charges of mutiny, Hornblower, Kennedy, and Bush convince an insecure and indecisive Lt. Buckland, now acting captain, that it would be appropriate to launch a surprise attack on the Spanish fortress at Santo Domingo. Matters are complicated when the inept Buckland incurs the enmity of the local rebels, who now regard them as enemies too. Captain Sawyer's increasing paranoia, deserting seamen, Buckland's growing jealousy of Hornblower, and the duplicity of the Spaniards all complicate the already perilous situation.

Finally promoted to Captain and given command of HMS Hotspur, Hornblower is sent to France to determine the status of Napoleon's pledge of peace, but instead he discovers Napoleon's troops waiting to invade. He also begins a romantic relationship with the young Maria Mason.

Soon after getting married, Hornblower is sent on a search and rescue mission for a British ship (under the command of an old friend) last reported off the French coast. In the midst of the search, the HMS Hotspur picks up some unwanted passengers and attempts to discover the objective of a small French invasion force.