Of all people, the archivist Sebastian Hellmann, who is unfit to live, is sent to Africa to search for the Marakunda - the largest diamond in the world, lost for many years, on which Cologne Cathedral originally rested and whose theft is causing the gradual sinking of the foundation. Time is pressing - Cologne Cathedral is in acute danger! For some time now, its façade has been crumbling alarmingly, it even threatens to collapse. Among them is the overly-integrated Cologne social worker Boris Penske, who is in danger of ending up in the cannibal cooking pot. So Sebastian can be glad that the equally energetic and pretty adventuress "Alex Jansen" accompanies him on his quest...