Sidney takes Geordie to Johnny Johnson's London jazz club, hoping to leave their worries in Grantchester for the night, but the backstage murder of Johnny's sister Claudette puts paid to that. When Archie, the victim's father and owner of the club, calls in a police officer pal to crack the case, Geordie immediately detects the copper is corrupt, while Sidney makes an important discovery about Claudette that she had kept hidden from all but those closest to her. As every lead seems to come back to Archie's violent past, recriminations within the family begin to play out.