Book — Richard Osman

It's the following Thursday.
Elizabeth has received a letter from an old colleague, a man with whom she has a long history. He's made a big mistake, and he needs her help. His story involves stolen diamonds, a violent mobster, and a very real threat to his life.
As bodies start piling up, Elizabeth enlists Joyce, Ibrahim and Ron in the hunt for a ruthless murderer. And if they find the diamonds too? Well, wouldn't that be a bonus?
But this time they are up against an enemy who wouldn't bat an eyelid at knocking off four septuagenarians.