After the war with France has ended in 1818, Captain Adam Bolitho is given command of the newly commissioned frigate Onward and sent to North Africa on a diplomatic mission to accompany the French frigate Nautilus in a show of solidarity. He knows he is lucky—the voyage should be easy; but Adam longs for a chance to marry the beautiful Lowenna and settle down on the Bolitho estate in Cornwall. Instead he must deal with the envy and ambition of his officers, hidden agendas among his men, and the former enemy's proximity. Then the Nautilus becomes a sacrificial offering on the altar of Empire, and the hunt is on for a treacherous foe. Suddenly every man must discover for himself whether the brotherhood of the sea can transcend old hatreds and an ocean of blood.