St. Vincent Halfhyde, commanding the steamer Taronga Park, is leaving Liverpool for the Amazon River. On board is a senior British diplomat charged with a delicate mission to Brazil, where the German Emperor is believed to be establishing a naval base from which to harass British shipping in the event of war. Halfhyde's voyage is plagued with clashes of personalities, with bad weather—and with murder. A horribly mutilated corpse is found aboard the Taronga Park in Liverpool Docks, but when Detective Inspector Todhunter of the Metropolitan Police is embarked to sail with the ship, Halfhyde is unclear whether the policeman's investigations are confined to the murder. More surprises await Halfhyde in Brazil, where he meets an old adversary whose unwelcome presence complicates the already volatile dealings with the South American authorities and with the sinister German Navy.