Five wide beer journeys through the Holy Roman Empire, four murdered brewers, three powerful dukes, and two Habsburg emperors lie on the path to a law that would endure for centuries: the Beer Purity Law. On his journey through the major beer cities of the 15th century, the imperial beer brewer Georg is on the trail of the secrets of his time: What does Emperor Frederick's mystical riddle AEIOU mean? Were there already consciousness-expanding drugs in the Middle Ages? And who murdered the brewers from four different cities? An epochal medieval crime story about Habsburgs, Wittelsbachs, and beloved beer.