My idea for the first book--"Grannies' Deadly Reunion"-- was that three grandmothers, who were friends in high school, get reunited some 30 years later and begin to kick over the traces of the disappearance of a high school girlfriend. Kids who were thugs in school had graduated to bigger crimes and weren't happy about these grannies sticking their noses into long-dead circumstances.
I continued the grannies theme into the second book--"Tunnel of Death." The setting moved from Chicago to San Francisco, but once again the grannies were tripping over dead bodies.
About this time I came to realize I wasn't really all that interested in writing about grandmothers.
The third book: "Looks Can Kill," was freed from the grannies theme, but continued the in the vein of criminal investigation by grey-haired, used-up human beings: This time it's a retired cop, Chet McGarey. And once again a reunion comes into play--aboard a cruise ship with a serial killer who is impersonating one of the high school mates.