Year 1495: In the medieval city of Zons, head of the City Guard, Bastian Mühlenberg, wonders how a place so idyllic could produce yet another vicious serial killer. From the shocking state of each new victim’s body, Mühlenberg determines the latest madman’s weapon of choice is a golden sickle. The hunt for the killer leads him into an underground maze in search of a treasure chest that his old friend Father Johannes guards the keys to. Can Mühlenberg beat the next swing of the sickle?

Present day: The last time he worked a serial killer case, Zons detective Oliver Bergmann found assistance―and love―in the form of journalist Emily Richter. Together they had solved a fatal puzzle by scouring Bastian Mühlenberg’s centuries-old notes, but apparently there’s more than one murderous history buff in Zons. When Emily’s best friend becomes a target, they must find what escaped their careful eyes in the last investigation―before the current killer fulfills his ghastly plan.