After some hesitation Buckland opens the captain's sealed orders and finds that the ship is to sail to Santo Domingo (Haiti) in the West Indies, where the Spanish are fighting a rebellion by the slaves. Buckland takes the ship into the harbour to destroy some Spanish privateers that are sheltering there, but he has lost the element of surprise and the Renown receives a severe mauling from the shore batteries on either side of the bay, runs aground, and is lucky to effect an ignominious retreat.
Buckland now intends to sail for Jamaica, but Hornblower manages to persuade him to allow a night raid to capture one of the forts that had bombarded them with red-hot shot during the abortive attack. The raid is led by Bush but its success is largely thanks to Hornblower. They capture both forts and take the Spanish garrisons away as prisoners, while the privateers' vessels are seized as prizes.
During the night the Spanish prisoners launch an attack to capture the ship. Bush is wounded and all seems lost, but Hornblower, who is in command of the prizes, leads a successful counterattack. The mad captain has been murdered by the attackers.
After they reach Jamaica Hornblower is promoted to Commander of a sloop, the Retribution. He is to return with her to England, where he is confident that his promotion will be confirmed. But by the time he reaches Portsmouth peace with France has been announced; his promotion has not been confirmed and he is laid off on half pay, with no prospect of resuming his naval career.
During his enforced inactivity Hornblower supports himself by playing whist, at which he is skilled. Not only does he make money in this way, he gets to know the senior naval people in the town. When the war with France is renewed his promotion is confirmed and he is once more given command of a sloop.
While there is, as usual, plenty of action, the underlying theme is Bush's changing relationship to Hornblower. At first Bush has suspicions about Hornblower's character and reliability, but by the end he has come to recognise his qualities as a leader and also as a friend.