The Alarm of the Black Cat by Dolores Hitchens

This classic mystery features a family feud, feline intervention, and the spirited septuagenarian sleuth from The Cat Saw Murder. A strange encounter with a little girl named Claudia and a dead toad sparks elderly detective fiction fan Rachel Murdock's obsessive curiosity, and she winds up renting the house next door just to see how things play out. But soon after she and her cat Samantha move in, Rachel realizes they've landed right in the middle of a deadly love triangle that's created animosity among the three families who now surround her. When Rachel finds Claudia's great-grandmother dead in her basement, she reaches out to a friend in the Lapd to solve the crime. They soon learn the three households have been torn apart by one husband's infidelity and a complicated will that could lead to a fortune. In a house plagued by forbidden love, regret, and greed, Rachel will have to trust her intuition, as well as Samantha's instincts, to survive-and keep Claudia out of the hands of a killer whose work has just begun.