Sidney's ex girlfriend Amanda is having an engagement party. He is loathed to attend but his sister wants him to attend and she brings her jazz loving black musician boyfriend, Johnny.
The party has a bunch of snobby people, a wannabe politician, bohemian Daphne and a married couple, William and Lillian. Amanda's wealthy father warns Sidney away as he can spot that he still pines for he.
Over the course of the evening the engagement ring goes missing and the black man gets blamed.
The next day the body of Lillian is found in the canal and her jewellery is missing that is eventually found on Johnny.
Geordie and Sidney team up hoping to exonerate Johnny but Geordie also figures that Sidney is in with these wealthy folks and will be useful.
There are red herrings and blind alleys but this murder might be a crime of passion with Johnny being framed. Sidney keeps mentioning that there are no coincidences when it comes to crime.
Like the BBC version of Father Brown, there is a modernist outlook to this 1950s set series. Not only a black boyfriend who becomes a convenient scapegoat but also the new curate Leonard is gay.
Geordie and Sidney have hit it off, they make a good team but Sidney has noticed that Geordie likes a drink.