Angie Russo is making coffee for a will reading at the law firm where she works as a paralegal when the ancient coffee machine delivers a shock that knocks her out. A few moments later, she’s hit with the overwhelming scent of tuna and hears a sarcastic male voice that soon reveals itself as belonging to … a cat. A cat sitting on her chest and staring into her eyes. A cat who introduces himself as Octavius Maxwell Ricardo Edmund Frederick Fulton, beloved pet of the recently deceased Ethel Fulton, who was brought to the will reading because he’s the recipient of a large bequest in her will. A cat who insists his adored owner was murdered: “I know it. I saw everything with my own two eyes.”
The firm has taken on a new associate, Charles Longfellow III, and assigned him what promises to be a no-win case: a local couple, Bill and Ruth Hayes, were slain in their soon-to-be-sold home, and there are no witnesses, only the circumstantial evidence that the slayings were committed with handyman Brock Calhoun’s hammer. But when Charles happens to catch Angie Face-Timing with Octo-Cat (there’s a fly in his Evian!), he grabs his one chance to prove his client’s innocence: have Octo-Cat interview Yo-Yo, the dead couple’s Yorkshire terrier, to see if he can help them find out who murdered his family. The feline agrees on one condition: that Angie owes him a favor.
Angie and Octo-Cat are moving into his former home — a mansion where the cat door opens automatically in response to a chip in his collar — when she hears that Senator Lou Harlow, who lived next door, was found at the bottom of her grand staircase. Turns out the suspects in Senator Harlow’s fall are … her two Sphinx cats, Jacques and Jillianne, who speak in rhymes.