Inspectors Ritter and Stark go into action when a dead body is found in the Berlin metro. The deceased is building contractor Horst Baumann, who became the focus of public attention not long ago when his company went bankrupt in spectacular fashion; after spending a long time abroad he has returned to the city and started a property redevelopment company together with his attractive wife Alissa and a mysterious associate by the name of Alsfeld. 
The investigation quickly puts the investigators on the track of a builder who was ruined when Baumann’s company went bust, Rothe. Was he determined to exact revenge?
While Stark discovers that there were serious problems in Baumann’s marriage - just before his death he and Alissa had had a furious argument – the search for the murderer leads Ritter back to the scene of the crime: the catacomb of tunnels underneath the city of Berlin. In the course of his enquiries he comes across Daniel, a social worker who looks after teenagers with educational problems and runs illegal tours through the underground labyrinth. And he isn't the only one who knows his way around them here: in the confusion of tunnels and shafts Ritter comes across an eccentric artist and hermit, Gregor. Both Daniel and the artist seem to be concealing some dark secret. Quite possibly a homeless woman could shed some light on the investigation; she has studied the murdered man had repeatedly in a video recording. But who is she? And where is she? Ritter and Stark are faced with a mystery both above and below ground.