Bavaria, 1886 King Ludwig II, infamous for his eccentric behavior, is declared insane by his government and removed from his throne. A day later, Ludwig's corpse washes up in the shallows of Lake Starnberg. Rumours about the cause of the tragedy abound, but few people know why Ludwig was really killed. Or what secret was silenced by his death. Germany, present day ... Hidden among the crates in a newly discovered Nazi bunker are documents stamped with a black swan, the insignia of the murdered king. As a favour to a friend, Jonathon Payne and David Jones fly to Bavaria to protect the documents, but soon face a life-or-death battle against an unknown enemy. From the depths of the Black Forest to the water canals underneath Ludwig's castles, the duo must solve the mystery behind the king's death or share his tragic fate.