Lieutenant Hornblower is the second novel (in the internal chronology) in the Hornblower series by C. S. Forester.
The newly promoted Hornblower joins HMS Renown as her fifth and most junior lieutenant. It soon becomes apparent that Captain Sawyer is mentally unbalanced, but any attempt to relieve him of command would likely lead to a charge of mutiny. One day, however, he apparently falls down a ladder (there are strong suspicions that he was pushed) and becomes so obviously deranged that Lieutenant Buckland assumes command.
Buckland is not up to the challenge. When his frontal attack on a fort fails miserably, it is Hornblower who devises a brilliant plan to defeat the Spanish privateers and accomplish their mission. On their way back to base, however, the prisoners take over the ship, capturing Buckland in his sleep and killing Sawyer. Hornblower organizes and leads a successful counterattack. Thus, when they reach port, it is he, not Buckland, who is rewarded with a promotion.
Best part of story, including ending:
It's a little intriguing that it's never made clear if Sawyer's fall was an accident. Some even suspect Hornblower.
Best scene in story:
After Hornblower returns to England (in command of HMS Renown), his promotion is rescinded due to peace breaking out. Bush runs into him in London and discovers he has to play whist to make a meagre living while hoping for an assignment.
Opinion about the main character:
During the court-martial over the loss and recapture of Renown, Hornblower modestly gives credit to his superior officers.