Rivers of London 3: Whispers Underground

Come Monday I get to do some proper policing. Person Unknown has been stabbed to death on the tracks at Baker Street tube. Magic may have been involved.'
Person Unknown turns out to be the son of a US senator and before you can say 'International incident', FBI agent Kimberley Reynolds is on DC Grant's case.
And down in the dark, in the tunnels of London's Underground, the buried rivers, the Victorian sewers, there are whispers of vengeance from beyond the grave.
DC Grant's latest case is about to come off the rails...