Prague at the end of the 16th century is terrified by leaflets from the mysterious Brotherhood of the Rosy Cross, which appear overnight on church doors. Their authors promise the coming of the day of enlightenment and the crushing of the devil of ignorance. However, the Jesuit Augustin Brecht sees them as an attack on his order and turns to the provincial court to find and punish the author of the leaflet. Court scribe Lukáš Trobl from Květnice is entrusted with the search for the mysterious brotherhood, but he takes little pleasure in his task. Nobody, not even the always well-informed imperial court physician Michael Maier, knows anything about the presence of the brotherhood in Prague. But soon someone starts murdering in the city and leaves a note with a pink cross and the letters R and K on his victims. Does this mean that the mysterious brothers are the perpetrators of these terrible crimes? Lukáš doesn't think so, rather it seems to him as if someone is settling accounts and taking advantage of people's gullibility. But how is he to find out the truth?