Vienna—June 1804. At the glittering debut of Beethoven’s Third Symphony, a Spanish diplomat meets with Captain Thomas Grey, agent of His Majesty’s Secret Service. In exchange for a gigantic bribe, the Spaniard discloses Spain’s darkest secret the actual terms of the Treaty of San Ildefonso with France. Spain’s neutrality in Napoleon’s war on Britain is only a ruse to keep the British navy from attacking the great treasure-armada now gathering in South America. Spanish warships will depart Montevideo, Uruguay, carrying 2,000 tons of gold; when the gold is safely in Madrid, Spain...